University of Plymouth

Matthew D Jones 3/26/2015

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Contents

Ethical Statement Page 2

Acknowledgements Page 3

Abstract & Title Page 4

Introduction Page 5

Materials & Methods Page 12

Results Section Page 18

Discussion & Conclusion Page 23

References Page 29

Appendices Page 31

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Ethical statement

Participants were informed about details of the experiment, but were not told

outstandingly that they would be tested for implicit and explicit memory performance

on relevant tasks. Participants were told they would be taking part in a simple picture

judgement and recognition task. Participants were selected using the psychology

pool of participant system whereby participants could sign up to the corresponding

studies. Here participants were informed briefly about the contents of the experiment

its duration and its value (monetary or points). Participants were required to give

signed and written consent upon arrival to their participation. Participants were then

given a brief, explaining the direction of the experiment and briefly its intentions.

Participants were not told exclusively the aim of the experiment to avoid any

confounding variables influencing the results. Participants were all informed they

could stop participating at any time throughout the study and would not be penalised

for doing so. Once the study had been completed participants were fully debriefed

and provided with an explanation of the experiment and its purpose; testing the effect

varying exposure duration has over implicit and explicit memory performance.

Participant’s personal information and the data recorded from the study are kept

completely confidential and will not be published to any public domain. Participants

were given forms with contact details of the experimenter and the project supervisor.

This allowed participants to make future contact to discuss any implications of the

research.

The data was collected using mat Lab, a program which allowed the replication of

Zago et al., (2005) study to materialise. All data was handled and retrieved by

Matthew David Jones. The data from each participant was input into Microsoft Excel

and subsequently IBM SPSS Statistics for further analysis.

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Acknowledgements

I would like to take this moment to thank someone whom was crucial to this project.

Dr. Chris Berry you have been an amazing supervisor. Chris is somebody who is

always on hand to meet and would regularly keep in touch and go the extra mile

supporting me in this project. I hope I have done myself and you justice in this paper.

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A behavioural account of how implicit and explicit

memory are affected by a variation of exposure

durations; do they derive from the same or different

neural mechanisms?

Matthew David Jones

10402968

University of Plymouth

Abstract

How does exposure duration of a stimulus affect implicit and explicit memory

systems? (Zago et al., 2005). To find out, we manipulated six exposure durations

(40, 150, 250, 350, 500 and 1900ms) and tested the performance of these durations

for both implicit and explicit memory. Our findings illustrate that priming initiates very

early on into the stimulus presentation and that longer exposure does not necessarily

consolidate a better representation of a stimulus. Elements of the “rise” and “fall”

phenomenon are present in our study and a clear threshold in priming magnitude is

observed (350ms).Similarities between explicit and implicit groups were witnessed

when both excelled in performance for a 1900ms exposure duration suggesting both

systems are closer related than initially anticipated.

(120)

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Introduction

The explicit memory system provides us with everyday memory; it is a verbal

conscious type of memory and primarily is used to recall experience. Explicit

memories are stored in chronological order and are sequenced together to create an

organized “file” of personal past experiences, consequently making a personal

unique history timeline. Explicit memory begins to develop at around 6 months old

(Nelson, 1995; 1997; 2000); however explicit memory does not reach full

development and become embedded into the human brain until the age of 5. Explicit

memories are often performed when re-calling everyday things such as ones

favourite birthday or holiday with the family. Implicit memory is the unconscious

memory system which is used to perform everyday activities that we execute over

and over again. For example, playing a sport; participating in the sport over

prolonged periods of time results in an improvement of performance which in turn

results in the activity becoming second nature, and consequently does not require

conscious thinking.

Research has indicated between the ages of 0-5 years, is the most impressionable

stage for implicit memory, requiring a safe and protected environment for implicit

memory to blossom wholly. If we repeat certain experiences multiple times we realise

that it becomes part of the implicit memory. These can be both positive and negative

so the need for a protective environment at an early stage is un-paralleled. Implicit

memory is largely sensation based, is mediated by the Amygdala and it is very

reactionary based and is a response to certain triggers (Knight et al, 2009).

Priming has been a major stakeholder in showing the effects of implicit memory. One

major discussion point amongst psychologists is its contrary results to those

witnessed in recognition tasks, which is testing our explicit memory, a conscious

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memory recall. The differing performance on the relevant tasks (priming vs.

recognition) do suggest that there is strong evidence pointing towards a double-

dissociation (Voss & Gonsalves, 2010). Participants exposed to a stimulus for a brief

period of time (250ms) yielded a higher rate of priming, whereas recognition

increased when participants were presented with a longer duration of stimulus

(2000ms), suggesting a relationship between encoding duration time and recognition

performance(Voss & Gonsalves, 2010).Despite a wealth of research that suggests

there is a double dissociation between priming and recognition, a strict criterion for

classifying dissociation (reversed associations) prevents research excluding a single-

process with multi-functions entirely (Dunn & Kirsner, 1988; Voss & Gonsalves,

2010).

Previous research has debated the source of both implicit (non-conscious) and

explicit (conscious) memory. The debate usually consists of disagreement with

regards to implicit and explicit deriving from the same single source, or a

multifunctioning memory mechanism, that can account for both types of memories

declarative and non-declarative. One such study that suggests implicit and explicit

memory came from two distinct separate neural substrates is the work by Crowder,

Robert G.; Mary Louise Serafine and Bruno H. Repp (1984). Crowder et al. (1984)

research employed priming procedures in the study to investigate possible effects of

isolating and testing solely implicit memory. Crowder presented the first half of the

participants with familiar American folk music whilst the other half were presented

with the same familiar American folk music’s melody but with an entirely new set of

lyrics played over the top of the melody. The first half of the participants, who were

exposed to familiar American folk music (with the genuine lyrics being played), had a

much higher chance and rate (0.92) of recognizing the music and labelling it as

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“familiar” than the second group. The second group who were exposed to “old words”

combined with a “new melody” showed a lower rate of recognition (0.78). From this

research it has been suggested that there is an implicit association being made in the

brain between the lyrics of the song and the melody of the song. Here, the memories

of the participants (able to recognize the American folk music) are implicitly creating a

single memory combining two separate entities; which are represented by both the

lyrics and the melody together, which later cannot be separated from each other. As

the participants in the second half of the research were exposed to a melody with

new lyrics over the top of it, recognition of the original song decreased. This suggests

that the brain’s memory systems couldn’t combine the two separate entities (the

melody and the new lyrics) together to form a memory that can be recognized and

retrieved as they have never been exposed to that melody alongside the set of new

lyrics. This was unlike the participants from the first half of the experiment as

mentioned previously, who were able to perform a higher rate of recognition as the

brain’s memory system had implicitly merged both the lyrics and melody to the same

memory. In the results Crowder et al. (1984) reports that a component is recognized

better when presented alongside the original context the component was presented

in, than when a component is presented alongside a new stimulus (page 294). It is

not the level of familiarity one has with the two contexts, but whether they have been

paired in the initial perception (Crowder et al. 1984: p294).

When considering the nature of the mechanism that drives both implicit and explicit

memory it is important to firstly gain an understanding of how the mechanism(s)

performance differs over time. If both explicit and implicit memories performance

deviate over differing time exposures it would suggest two differing neural substrates.

It has been suggested that behavioural priming performance maxes out at around

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250 Ms for a previously encountered stimulus and then performance begins to

decrease as the duration of prior exposure to a stimulus increase. This in psychology

is referred to as the “rise” and “fall” phenomenon. This display of a “rise and fall”

pattern in behavioural priming has been witnessed in varying stimuli exposure

duration (Zago et al., 2005). It has been found that duration to a stimulus as low as

40 Ms (and lower) has yielded significant influence in improving priming performance.

This brief period of exposure (40 Ms) has shown a better performance in behavioural

priming than when the stimulus presentation was of a lot longer duration (Bar and

Biederman, 1998; 1999). Other studies that have investigated the duration effect on

behavioural priming support the result from Zago et al., (2005). One example of the

“rise” and “fall” phenomenon that supports the results of Zago et al. (2005) was the

research conducted by Crabb and Dark (1999;2003, experiment 2). This research

yielded similar results and displayed a “rise” when the exposure duration increased to

200ms but “fell” when the duration was increased up too 300ms. Crabb and Dark

second study (2003) showed that a further “fall” was witnessed when the duration

rose to 600 Ms and fell furthermore when duration of a prior stimulus rose again to

1000 Ms. Other research that looks into whether implicit memory is affected by

exposure duration again found corresponding results with Zago et al. (2005). A

shorter presentation of priming led to an increase in performance of behavioural

priming whereas longer exposure to the stimulus caused weaker behavioural priming

performance and even caused negative priming to occur (Barbot & Kouider, 2012;

Faivre & Kouider. 2011; Huber & O’Reilly, 2003). The reasons for this “rise” and “fall”

effect with regards to priming is unclear but an attempted explanation has been put

forward by Zago et al. (2005). Zago et al. (2005) proposed the cross model of

“selection” and “sharpening”.

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“Selection” (Wiggs & Martin 1998) uses the important features of a stimulus as the

representation of that previously viewed stimulus, whilst discarding any non-essential

information. Selection occurs more prominently with extensive exposure duration to a

stimulus, selection operates on a high-level information and semantic knowledge. As

this “selection” model is being used, a small overlap between the features within the

representation of the stimulus and the target stimulus actually decrease, causing a

decline in priming. “Sharpening” is the second aspect of the combined model

proposed by Zago et al. (2005) to explain the “rise” and “fall” of priming. “Sharpening”

however suggests that neurons in the inferior temporal cortex represent only global

properties at 130 Ms but then the coding becomes more specific from 130 Ms

onwards and is stimulus specific at around 240 Ms (Tamura & Tanaka, 2001).

Despite this, the “sharpening” aspect of the cross model, is not widely accepted and

credited as the explanation for the “rise” and “fall” of priming.

Still, there does remain a large amount of empirical evidence that can be interpreted

to represent a single multi-functioning mechanism in the brain used for memory

across all functions. One example would be damage caused in the brain to the

medial temporal lobes (MLT); this was shown to hinder both implicit and explicit

memory. Now, although the explicit memory function and performance was hindered

more extensively than the implicit function, the fact that two “opposite” functions

(conscious and sub-conscious) are impacted by the same physiological component

does suggest that there are some overlaps between the two (Berry et al. 2014). One

interpretation of the research by Berry et al., (2014) is that because the MTL in the

brain region was damaged and consequently did affect both the abilities in explicit

and implicit memory tasks, then it would be logical to suggest that the two behave

similarly and would likely to be from a single multi-functioning system. If this was the

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case and both explicit and implicit memory were both driven by a single system, it

would be expected that the performance over differing stimulus exposure durations

would be also similar. However, the fact that these two entities are both divided by

consciousness, they should rather act in mirror parallels of each other.

The primary concern when looking at stimulus exposure duration on explicit and

implicit memories is the repetition-related response. Repetition-related response

according to Zago et al., (2005) by definition is “associated with the level of

experience an individual has with a particular stimulus “. Despite this clear definition,

the manner in which it holds the relationship between stimulus duration and cortical

representation is somewhat absent. This was the main impetus behind the start of

the experiment and consequently stimulus duration was manipulated. The aim of the

current research was to investigate the effects of study exposure duration on

repetition priming and recognition memory. Participants were split into two conditions

and would be taking part on the conscious explicit memory task or the non-conscious

implicit memory task. The two conditions were both split into two identical sub-

conditions, which consisted of 6 sub conditions. Here the exposure duration was

manipulated between six differing durations .The research in question used a method

very similar to that witnessed in Zago et al. (2005, p 1656) however there were a few

adaptations that took place. The difference in the present investigation was that: One

of the groups completed a procedure to measure the performance of implicit memory

by using the semantic judgement task (known as the priming condition). The second

study group completed an explicit memory task known as the recognition task.

However, despite this interest on the varying performance of implicit memory, little

investment has been made on examining how explicit memory and recognition is

influenced by a change in stimuli exposure duration. Assuming that implicit and

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explicit memory both derive from two distinct separate neural entity’s, that both

function in the opposite manner (consciously and sub-consciously) and considering

the results of previous research, it is logical to hypothesize that; as the exposure

duration to a stimulus increases, so does the performance of behavioural priming (up

to a threshold of 250 Ms). Once the threshold has been breached performance in

implicit memory tasks decreases .In contrast to implicit memory performance, the

second hypothesis assumes that as exposure duration to a stimulus increases the

performance on the explicit memory task (recognition) will also increase, this is

because subjects will have more time to consciously observe and “learn” the words. If

exposure duration to a stimulus does increase the performance of conscious

recognition and recollection and then exposure duration beyond 250 Ms hinders

behavioural priming performance, then it would suggest that there are two distinct

neural mechanisms at work with regards to explicit and implicit memory.

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Materials and Methods

Participants

A total of 20 participants participated in our experiment. The mean age of the

participants in the implicit memory condition was 19.6 years and for the explicit

memory group the mean age was 23 years. In total there were 7 males and 13

females. These participants were recruited by using an opportunity sample from

Plymouth universities psychology pool website, consequently making all participants

psychology students. The participants were split into two separate groups, equally

divided so there were 11 participants in each condition. All participants had given full

written consent to partake in this study prior to the research. The Plymouth University

Ethics Committee granted ethical clearance for this experiment.

Stimuli and Apparatus

The stimuli used in this study were 425 pictures of familiar objects such as elephants,

tools, glasses, vehicles and food (Fig. 1). The dimensions of the images presented to

the participants on a computer screen with a plain white background were recorded

at 6cm height x 6cm width. These 425 images were randomly allocated to the

following conditions: 60 pictures x 6 repeat conditions (40, 150, 250, 350, 500 and

1900ms), 60 pictures x 1 new condition (to appear in the semantic judgement task

once only). As this experiment was an adapted replication of Zago et al. (2005), the

same 10 masks seen in Zago et al’s experiment were used here. These masks

consisted of very random images creating what is referred to as a “nonsense” image

that is not relatable to the object stimuli.

The images were appearing on the computer screen that was measured at 22”.

Participants were required to respond to judgements during the experiment by

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pushing the relative button on the keyboard: “N” for natural, “M” for manufactured,

specific for the priming condition. Also, the numbers keys: 1, 2, 3 and 4 were required

for a confidence rating in the recognition condition.

Fig. 1

Here are some of the stimuli that participants saw. For the recognition condition

participants were required to make a judgement on their confidence rating’s as to

whether the image had been previously presented or not. In the priming condition, a

participant simply was required to make a judgement on whether the image on the

monitor was a manufactured object or is a naturally occurring object.

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Design and Procedure

There were six different stimuli durations that each participant completed regardless

of condition. These six durations were 40, 150, 250, 350, 500 and 1900 Ms. Each

trial had a duration set at 2 seconds or 2000 Ms. In total there were 13 different

conditions for the object presentation. Both recognition and the priming condition had

the same 6 different exposure conditions and the same repeat condition that was set

at 500 Ms. At this point, a judgement was required from the participant again

dependant on which condition the participant was selected for. The total trial duration

as aforementioned is 2 seconds. The two-second period consisted of object

exposure duration that varied (40, 150, 250, 350, 500 and 1900 Ms) and the mask

duration that also varied. Hypothetically if the object were presented for 500 Ms then

the mask would be presented for 1500 Ms. The mask also symbolized the start and

end of that specific trial.

Priming Group

The implicit memory task that participants were required to complete in this condition

was a semantic priming task. The implicit memory task was measuring priming

performance and the independent variable was the stimulus duration. Images that

were presented once or only twice were intermixed and amongst other images that

had been previously repeated for multiple trials. The participants had a blank screen

with nothing but a single fixation point (‘+’), which was presented in Arial 28pt on the

screen. This was to be presented at the centre of the screen for 500ms duration.

Where the fixation point was situated, was the location that the images appear during

the continuous stream in the study phase. Each object was presented to the

participant on the monitor in front of them for a randomly selected duration (40, 150,

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250, 350, 500 & 1900ms). Post the image being presented, the mask immediately

followed and represented the start and end of a trial. The masks were presented for

differing durations. One of the 10 masks was randomly selected on each trial to be

presented for the remainder of the 2000ms trial. Hypothetically, if the participant was

shown an object that was displayed for 500ms, then the mask would be present on

the screen for 1500ms, confirming that the total trial duration is at 2000ms. The

streams of images were consisting of either naturally occurring objects or

manufactured ones. The job of the participant was to realise and make a judgement

as fast as possible as to which of the two categories the object in question falls into

(as seen in figure 3 in the appendix). As aforementioned each trial lasts for a total

duration of 2000ms. After an item was presented for its specific exposure duration

(40, 150, 250, 350, 500 & 1900ms), a mask (nonsense image) was presented for the

remaining duration of the 2000ms trial. The trials were presented consecutively one

after the other, creating a constant stream of images appearing. Every block of 130

trials that the participant completed, signalled the start of 15 second break to allow

the participant to again prepare themselves.

Recognition Group

The explicit memory task that participants were required to complete in this condition

was a simple recognition task; the independent variable again was the stimulus

exposure duration. The participants had a blank screen with nothing but a single

fixation point (‘+’) which was presented in Arial 28pt on the screen. This was to be

presented at the centre of the screen for 500 Ms duration. Where the fixation point

was situated, was the location that the images appear during the continuous stream

in the study phase. The study phase consisted of 360 images. Again, the same

intervals between stimulus trials were set; each trial totalled up to duration of

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2000ms. The total duration of each independent trial was 2000 Ms, the 2000 Ms was

made up of the stimulus duration which could be set at: 40, 150, 250, 350, 450, 500

or 1900 Ms, the remaining length of time would be made up by the mask (nonsense

image), completing the 2000 Ms elapsed time. The difference between the

recognition group and the priming group is the way that the test phase was

conducted. The participants in the recognition group were asked again to make a

judgement but instead were rating their confidence against whether the image

presented in front of them had been seen before in the study phase. The participants

were presented with a choice of four keys to hit (as seen in figure 4 in appendix). The

choices were high and low confidence ratings that the image wasn’t presented

before. The other two options were high and low confidence ratings on whether the

image had appeared before. During the test phase for the recognition group, the

participants were presented with a total of 150 items, 90 of which were old items

whilst 60 of them new items previously unseen to the participant.

The whole procedure was running for an approximate 25-30 minutes for both

conditions. A smaller number of stimuli were used in the recognition condition to keep

the duration of both priming and recognition conditions the same. Participants were

fully briefed prior and debriefed post the research. The experiment began with the

participant’s being able to partake in practice trials prior to the study commencing.

These practice trials gave the participant time and a chance to understand what was

expected of them through the duration of the study. Figure 2 shows the computer

screen image that the participants were presented with at the start of the study. Here

the participants are told that they are taking part in a categorization task. They were

informed that a series of images were to be presented in succession, alongside these

images, they were presented with a judgement; whether the image on the screen

17

was manufactured or was a natural object. Participants were informed that they

should aim to be as quick and concise as possible throughout the research.

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Results

Our main findings are that: (i) with the increased magnitude of exposure duration to a

particular stimulus an increase in recall ability was profound, it should be said that the

increase in exposure duration facilitated the consolidation of a stimulus in conscious

recognition and (ii) that an increase in the magnitude of exposure duration in the

priming task displayed a variety of performance patterns; Most notably a decline in

performance on the 150,250 and 500ms conditions whereas the 40, 350 and 1900ms

conditions showed an increase.

Behavioural Results

On average the difference in mean response time (RT) in the priming task varied

greatly between the six conditions (40,150,250,350,500 & 1900ms). A repeated

measure ANOVA was conducted and specified that exposure duration (as witnessed

in the experiment) produced a significant effect on the behavioural priming task F (1,

9) = 12.95, p = 0.006, however it was not significant across the whole experimental

design and conditions F (5, 45) = 2.81, p = 0.27 (Fig.10). On the recognition task a

repeated measure ANOVA was also conducted and specified that there was a

significant effect for exposure duration on the recognition performance F (1, 9) =

33.55, p = 0.00** and was also significant across all conditions F (5, 45) = 3.80, p =

0.006.

A one sample t-test was conducted on the exposure durations for both memory

types, implicit and explicit. For the implicit memory group, the 6 exposure duration

conditions produced the following statistics; 40ms condition (M = 37.80, SD = 39.18),

150ms condition (M = 29.22, SD = 28.76), 250ms condition (M = 31.18, SD = 32.62),

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350ms condition (M = 46.10, SD = 38.59), 500ms condition (M = 22.34, SD = 25.66)

and the 1900ms condition (M = 43.03, SD = 39.05).

The explicit memory group data also underwent a one sample t-test for the same 6

exposure duration conditions and produced the following statistics; 40ms condition

(M = 0.31, SD = 0.20), 150ms condition (M = 0.34, SD = 0.25), 250ms condition (M =

0.43, SD = 0.25), 350ms condition (M = 0.41, SD = 0.23), 500ms condition (M = 0.42,

SD = 0.26) and the 1900ms condition (M = 0.52, SD = 0.29).

Effect of exposure duration on priming performance

To be able to evaluate the effect that previous exposure to a particular stimulus has

on the performance of behavioural priming, priming values were calculated by

subtracting the response times (RT) participants provided in the repeat condition

from the RT’s for the new condition. The results obtained accept the null hypothesis.

The briefest exposure duration of 40ms produced the third largest mean difference in

reaction time between items presented “new” against items that were “repeated

(37.82). However, unlike previous research, the performance of priming was

hindered by an increase of exposure duration to a stimulus up to 150 and 250ms,

when this exposure duration was increased to 350ms; the largest difference in RT

between new and repeated stimuli was produced (46.09). However, when the

exposure duration increased up to 500ms, the RT between new and repeated stimuli

dropped (29.21) to the lowest score. However, when the stimulus exposure duration

reached the longest period of 1900ms, the difference was again large and

behavioural priming performance was increased (43.04). Furthermore, T-tests

showed that 1900ms of previous exposure to a stimulus caused a greater magnitude

of priming than all the other conditions. Despite that, exposure at 40ms caused a

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greater magnitude of priming than 150, 250 and 500ms of exposure. This suggests

only brief exposure is necessary for behavioural priming to develop and perform

effectively, however the results also indicate that the prolonged exposure condition

also contributed to an increase in priming performance more so than the 40ms

condition and the 350ms condition.

Fig 2. Behavioural data. The mean magnitude of priming calculated by deducing the mean RT for old objects from the response time of new objects. Maximal priming was observed at 350ms.

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40 ms 150 ms 250 ms 350 ms 500 ms 1900 ms

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Priming performance over 6 exposure durations

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Effect of exposure duration on recall ability

To be able to successfully evaluate the effect differing exposure durations had upon

recognition performance, scores for recognition performance were calculated with the

use of the “hit” and “false alarm” method. A “hit” is where a participant correctly

identifies the stimuli presented on the screen in front of them as either new or old. A

“false alarm” is where a participant incorrectly labels a new image old or old image

new. The difference in scores between “hits” and “false alarms” was used as a

measure of performance on recall tasks. Therefore the higher the difference between

the two scores, the better the recall performance.

As witnessed in the statistical analysis for the recognition task, a significant positive

correlation was found between exposure duration and recall performance. Because

there was an increase in exposure duration, the performance on the recall task

invariably, also increased. This rejects the null hypothesis supporting the notion that

as a stimulus is presented for a longer duration, consciously, it becomes easier to

recall information about that episode at a later time. The scores progressively

increased with exposure duration. The briefest exposure duration was 40ms and as

expected scored the lowest in terms of difference between the “hit” and “false alarm”

rate (0.31). The second lowest duration (150ms) scored a difference of 0.34, this was

as expected, an improvement upon the previous exposure duration. The 250, 350

and 500ms all scored very similarly, scoring 0.43, 0.41 and 0.42 respectively. Finally

the highest scoring exposure duration condition for recognition testing explicit

memory was the 1900ms condition.

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Fig 3. Behavioural data for the mean magnitude of recall performance; this was

calculated by deducing the mean false alarm rate from the mean hit rate. Maximal

recognition ability was induced from the 1900ms stimulus presentation.

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40 ms 150 ms 250 ms 350 ms 500 ms 1900 ms

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Recall ability over 6 exposure durations

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Discussion

The present study intended to investigate whether exposure duration had an effect

on implicit and explicit memory performance. The procedure displayed a clear

difference in the way implicit and explicit memory respond to varying exposure

durations. The results demonstrated that varied exposure duration in the implicit

memory group caused varying magnitudes of priming whereas the explicit memory

recognition task produced a positive correlation between exposure duration and

recall ability. The results support the observation by Bar and Biederman (1998; 1999)

that prominent levels of priming are present even when a stimulus is presented for a

brief exposure duration. Notably, Perfetti and Bell (1991) also found significant levels

of priming to be present after a 45ms stimulus presentation .In our results, high levels

of priming were present after 40ms, supporting the notion that priming is extremely

prevalent even after brief exposure.

The present results demonstrate that in the implicit memory group, the 350ms

condition facilitated the maximal magnitude of priming. The threshold level is said to

be the point at which the cortical object representation is at its maximum .The

threshold value in our study for priming magnitude is not witnessed across much

previous research, whereby thresholds for maximal priming have been reported to be

set around the 200ms mark for stimulus duration (Crabb & Dark, 1999; 2003,

experiment 2). Larger thresholds have also been reported but only up to 250ms

(Zago et al., 2005). Despite the differences in threshold values, the present study

does present mutual trends with previous research investigating exposure duration.

For example, the magnitude of priming decreasing once the threshold value has

been breached (Crabb & Dark, 1999; 2003) is reflected in this study. Priming

magnitude was at its strongest in the 350ms condition (46.09) and then weakest in

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the subsequent 500ms condition (22.34). This deviation in magnitude of priming is

referred to as the “rise” and “fall” phenomenon and is prevalent in the present study.

Despite features of “rise” and “fall” being present, aspects of the data fail to support

this phenomenon. For example, stimuli presented for 350-1900ms produces a

weaker priming magnitude when compared to the priming magnitude produced by

stimulus exposure duration between 40-250ms (Zago et al., 2005). This is contrary to

the results in the present study which exhibit large priming effects for exposure

durations post the threshold (1900ms) and little priming effects for exposure

durations prior to threshold, excluding the brief 40ms condition. Consequently, it

would be more appropriate to assume the way magnitude priming behaves over

varying exposure durations is not represented reliably in this study. Despite this,

similar phenomenon’s such as the “rise” and “fall” effect and priming being present

post brief exposure to a stimulus are still prevalent in the present study.

Another phenomenon that is associated with implicit memory is “fine-tuning”. Fine

tuning is a function that is part of the “sharpening” process used in implicit memory to

preserve and consolidate key characteristics of a stimulus for future identification

(Zago et al., 2005). Fine-tuning occurs early into the presentation of the stimulus.

With the use of fMRI, activity in inferior temporal coincides with the fine-tuning

function and begins to instigate at 130ms into the stimulus presentation and is

functioning at its optimal level around 240ms into the stimulus presentation (Tamura

& Tanaka, 2001). This is the around the same duration into stimulus presentation that

the threshold for priming performance is realised, suggesting that the two are

coexistent. In our research, the 350ms condition is the threshold peak, which would

mean that the fine-tuning process is functioning at optimal capacity when stimulus

presentation lasts 350ms.

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However, it would be inappropriate to directly state our findings support the fine-

tuning phenomenon because magnitude of priming should increase until the

threshold peak is reached, however the results indicate that priming magnitude

declined between 150-250ms. Priming strength was higher at 40ms (37.82) than the

subsequent 150ms (29.21) and 250ms conditions (31.18). However, our results

should not be interpreted entirely as having an absence in fine-tuning but rather the

continuum of priming scores reflecting fine-tuning, were not performing in a

“traditional” manner as reported by Tamura and Tanaka (2001).

Results from the explicit memory group show that as exposure duration increases as

does the performance on the subsequent recognition task. This is consistent with

previous findings that state the duration of rehearsal has a significant increase on

recognition task performance (Greene, 1986) and other explicit memory tasks

(Debner and Jacoby, 1994). Another factor that influences conscious recollection is

the number of studied items, the larger the number study items, the weaker the

consequential recall (Mandler, 1985). Although this can reduce the performance of

conscious recollection, this confounding variable did not contaminate our results

because the numbers of studied items were standardized. Therefore, the effect

witnessed was a direct result of exposure duration manipulation.

The explicit memory group reacted very different to the varying exposure durations in

contrast to implicit memory. Unlike the implicit memory condition, a threshold peak is

not present in the explicit memory group. For the explicit memory condition there is

no optimal exposure duration, the only relationship is as duration increases,

recognition also surges. However, there are some mutual aspects of implicit and

explicit memory performance to varying exposure duration in the present study.

Unexpectedly the 1900ms condition produced the second largest priming score out

26

of the six conditions. This was an unforeseen effect as priming performance is meant

to decrease post the threshold being breached. Similarly, the condition with the

highest recall rate was the 1900ms condition. As a similar trend has been witnessed

for both memory types when exposed to a 1900ms stimulus, it would seem logical to

suggest both types may coincide, this interpretation suggests either; (i) after an

exposure duration has been breached, conscious memory aids implicit memory

function, or; (ii) explicit and implicit memory come from the same source and act

more similar than initially anticipated. This supports research concluding that regions

in the brain that specifically contribute to explicit memory, such as the hippocampus,

are activated during implicit memory tasks (Henke, 2010). Furthermore, implicit

memory, despite being completely independent from other forms of memory, actually

interacts with many types of memory (Tulving & Schacter, 1990).This high score of

priming in the 1900ms condition could reflect a behavioural effect of conscious

memory influencing implicit memory, or represents an overlap between conscious

and non-conscious memory sources.

This is a plausible suggestion as it’s not the first time implicit memory has been

potentially contaminated by the influence of explicit memory involuntarily (Klavehn et

al., 1994). An example would be when a participant becomes conscious that the

stimuli have been previously presented to them, causing explicit memory to aid their

judgement. This is a possible explanation as to why the 1900ms condition produced

such a high level of priming magnitude. As reported by Berntsten (2010), involuntary

explicit memory recall can develop with the observation of a stimulus that acts as a

cue. Although ecologically valid to real life circumstances, such as witnessing an

advertising board that caused a conscious memory of an experienced life event, the

present study can be considered to represent a behavioural response to the

27

contamination of implicit memory by conscious memory under controlled settings.

The high priming magnitude for the 1900ms condition supports the claim by Cabeza

& Dew (2011) whom suggest that implicit and explicit memory is initiated by the

repetition of stimuli and that a threshold is breached and when breached, priming

converts itself into a conscious “signal of oldness” (Page 180). If hypothetically

correct our research shows a potential point of transition between sub-conscious

priming into conscious recall occurs between 500ms-1900ms from stimulus onset.

The results suggest a clear difference in the performance of implicit and explicit

memory over varying exposure durations. Differences in behaviour over time,

suggests both types of memory derive from a multiple memory system that supports

each type individually. The results can be interpreted to support a multiple model

system; the implicit memory performance reflects procedural memory because

priming was present even with duration of 40ms. Even though the reversed U-shape

arc which is what is expected to be present when displaying priming over differing

exposure durations was not achieved, the two (explicit and implicit memory) behaved

contrastingly to each other. This supports previous models that divide memories by

level of consciousness (Squire & Knowlton, 1995; Squire, 2009). In contrast to

implicit memory, the explicit memory condition showed examples of how it revolves

around declarative memory. This was shown by the increase in performance being a

direct result of an increase in exposure duration. This is because an opportunity to

create a more distinctive traceable memory is presented, allowing the memory

system to attain more key components and detail from the stimulus, creating a more

memorable object representation. Future research should investigate the possible

activation of conscious memory aiding implicit memory and which factors such as

exposure duration create this effect in the human memory system.

28

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30

Appendix

Fig.1

Displaying the opening screen to the study that participants witnessed. Here, they

were instructed by the computer, what to expect from the study and what each trial in

the research was like.

Fig.2

This is the option screen participants in the priming group are faced with. Here they

are required to make a judgement on whether the image on the monitor is natural or

manufactured. They can make the judgement by pressing ‘Q’ and ‘P’ for natural and

manufactured objects respectively.

31

Fig.3

This is the screen that the participants in the recognition group were presented with

on the test phase of the study. Here they were required to provide us with a choice of

confidence ratings. The choices as seen below were; high confidence or low

confidence that the image had been seen before and again, high confidence and low

confidence that the image had not been seen before. Accuracy is the primary target

here.

Fig. 4 this table shows the Means and Std. Deviation scores produced by the

statistical analysis (repeated measures ANOVA) on the implicit memory priming task.

Descriptive Statistics

Mean Std. Deviation N

dur40ms 37.8000 39.17896 10

dur150ms 29.2200 28.76069 10

dur250ms 31.1800 32.62061 10

dur350ms 46.1000 38.59370 10

dur500ms 22.3400 25.66339 10

dur1900ms 43.0300 39.04516 10

32

Fig.5 this table shows the Means and Std. Deviation scores produced by the

statistical analysis (repeated measures ANOVA) on the explicit memory recognition

task.

Descriptive Statistics

Mean Std. Deviation N

dur40ms .3080 .20004 10

dur150ms .3360 .25444 10

dur250ms .4270 .24864 10

dur350ms .4080 .22905 10

dur500ms .4240 .25605 10

dur1900ms .5220 .28809 10

Fig.6 this table is a product of the repeated measures ANOVA; it displays significance levels for the between-subject effects for implicit memory.

Tests of Between-Subjects Effects

Measure: MEASURE_1

Transformed Variable: Average

Source Type III Sum of

Squares

df Mean Square F Sig.

Intercept 73269.181 1 73269.181 12.945 .006

Error 50939.294 9 5659.922

Fig.7 This table is a product of the repeated measures ANOVA; it displays the significance levels for the between-subject effects for explicit memory.

Tests of Between-Subjects Effects

Measure: MEASURE_1

Transformed Variable: Average

Source Type III Sum of

Squares

df Mean Square F Sig.

Intercept 9.801 1 9.801 33.551 .000

Error 2.629 9 .292

33

Fig.8 This table again was produced by the repeated measures ANOVA test and

displays to the significance levels of the implicit memory priming task, using the

Sphericity Assumed statistical analysis option.

Fig.9 This table again was produced by the repeated measures ANOVA test and

displays to the significance levels of the implicit memory priming task, using the

Sphericity Assumed statistical analysis option.

Tests of Within-Subjects Effects

Measure: MEASURE_1

Source Type III Sum of

Squares

df Mean Square F Sig.

exposureduration

Sphericity Assumed .287 5 .057 3.804 .006

Greenhouse-Geisser .287 3.824 .075 3.804 .012

Huynh-Feldt .287 5.000 .057 3.804 .006

Lower-bound .287 1.000 .287 3.804 .083

Error(exposureduration)

Sphericity Assumed .679 45 .015

Greenhouse-Geisser .679 34.418 .020

Huynh-Feldt .679 45.000 .015

Lower-bound .679 9.000 .075

Tests of Within-Subjects Effects

Measure: MEASURE_1

Source Type III Sum of

Squares

df Mean Square F Sig.

exposureduration

Sphericity Assumed 4037.891 5 807.578 2.806 .027

Greenhouse-Geisser 4037.891 2.154 1874.727 2.806 .082

Huynh-Feldt 4037.891 2.854 1414.843 2.806 .062

Lower-bound 4037.891 1.000 4037.891 2.806 .128

Error(exposureduration)

Sphericity Assumed 12950.624 45 287.792

Greenhouse-Geisser 12950.624 19.385 668.085

Huynh-Feldt 12950.624 25.686 504.199

Lower-bound 12950.624 9.000 1438.958

34

Fig.10 This is a graph displaying the difference in mean RT for new and old items for

varying exposure durations. This was completed by subtracting the mean RT for new

items away from the mean RT for old items.

35

Fig.11 This is a graph displaying the difference in correctly identifying the presented

stimulus as new or old against incorrectly labelling the stimulus new or old, for

varying exposure durations. This was completed by subtracting the “hit rate” away

from the “false alarm rate”.

36

Fig.12 The brief participants were presented with prior to the study commencing.

The University of Plymouth Faculty of Health and

Human Sciences

Brief

In this study you will be presented with a series of images one after the other on a

computer screen in front of you. All experimental instructions will be clearly provided

on the screen. You will be given 5 practise trials for every test phase encountered. If

you have any questions about the research do not hesitate to ask the experimenter.

The experiment should last around 30 minutes.

You will be provided with an informed consent sheet if you choose to agree to

participate in the research.

Contact details are provided should you require any answers about the research in

the future.

Contact Details:

Researcher: Matthew D Jones

Phone Number: 07801922320

Email: matthew.d.jones@plymouth.ac.uk

Supervisor: Christopher Berry

Supervisor Email: Christopher.berry@plymouth.ac.uk

37

Fig.13 Debrief participants were given post the studies completing, this was used to

inform the participants of the actual aim of the research and why it was a necessary

piece of research.

The University of Plymouth Faculty of Health and Human Sciences

Debrief

This study was an investigation into the behavioural differences between explicit and

implicit memory and the effect that exposure duration to a stimulus has upon the

performance of both of types of memory. The research undertaken was an

adaptation of Zago et al. (2005) research. The aim of the experiment was to

understand the difference nature of performance for both implicit and explicit

memory. The route of memory in the brain and its nature is a highly disputed area of

psychology, this research attempts to provide substantial findings that can support

either a single multi-functioning system, or two separate functioning systems entirely.

In the experiment, you the participant, were exposed to a series of images each

presented differently depending on which exposure duration condition you were

assigned too (40, 150, 250, 350, 500 &1900 Ms.) For the first part of the study you

were required to recall as many images as you possibly could from the series

presented previously. This is specifically testing your explicit memory system by

recognition. For the implicit memory test, priming was administered. Another series of

images were presented during the study phase and then on the test phase, the

participant is required to select “yes” or “no” to the question, “has this image been

seen before?” This is a test of your implicit (unconscious) memory. The purpose of

differing stimulus durations for each task on both explicit and implicit memory was to

examine the difference in performance for each over the same stagnated duration

blocks. Any significant change in performance from either from the other, would

suggest that they are two differing systems entirely and are not originated from the

same multi-functioning source in the brain. It is hypothesized in the research that

likes Zago et al. (2005), priming performance increases with exposure duration up

until the threshold of around 250 Ms, soon after and beyond this, performance will

begin to decline. As for the explicit memory task of recognition, it is expected that the

longer the stimulus duration, the increase in recognition performance. If both are

apparent in the results of this research, it does suggest that there are two distinct

functioning mechanisms in the brain in charge of implicit and explicit memory

respectively.

Please contact the researcher Matthew Jones at

matthew.d.jones@students.plymouth.ac.uk if you have any queries about the

research in any capacity.

Contact Details

Researcher: Matthew Jones

Telephone number 07801922320.

Supervisor: Dr Christopher Berry chris.berry@plymouth.ac.uk

38

Fig. 14 the consent form participants were given upon arrival to the study. Signature

gives the experimenter the participant’s permission to take part in the research and

collect the data.

RESEARCH INFORMED CONSENT FORM

Title of Project: Simple picture judgement task, manufactured or natural?

Investigator(s): Matthew David Jones

Researcher Email: matthew.d.jones@students.plymouth.ac.uk

Please read the following statements and, if you agree, sign on the

corresponding lines to confirm agreement:

I confirm that I have read and understand the information sheet for the above study.

I have had the opportunity to consider the information, ask questions and have had

these answered satisfactorily.

I understand that my participation is voluntary and that I am free to withdraw at any

time without giving any reason.

I understand that my data will be treated confidentially and any publication resulting

from this work will report only data that does not identify me.

I freely agree to participate in this study.

Signature: …………………………………………….

Name of participant (block capitals)

Signature: …………………………………………….

Date

…………………………………………….

Researcher (block capitals)

Signature: …………………………………………….

Date

…………………………………………….