PERCEPTION OF THE FLASH-LAG EFFECT

Maksims Ivanovs University of Tartu / University of Latvia

Advisor: Jaan Aru

Introduction

• The flash-lag effect:http://www.michaelbach.de/ot/mot-flashLag/index.html• Most likely caused by the neural delays in

arrival of photoreceptor signals from retina to visual cortical areas

• Threshold: 1 rpm / 2 rpm• Why it is important

The Present Research

• Purpose: to study possible effect of gender, age, education

• Hypotheses– Gender has an effect on the threshold – Age has an effect on the threshold– Education has an effect on the threshold

• Data gathering: a large-scale online survey

Survey

• The pilot study: 8 participants• Design:– 3 parts: introduction, the questions regarding the

perception of the visual stimulus, the questions regarding the participants himself / herself

• Two orders of the stimuli:– 10, 15, 5, 4, 3, 2, 1 rpm– 10, 5, 4, 3, 2, 1, 15 rpm

• Three languages: English, Latvian, Russian• All in all – six versions

Administering the Survey

• Facebook, email• Personal contacts• Facebook groups:

– ESN Tartu Spring 2014– Neuroscience– Psychology

• Forwarding via email to the students:– UT Faculty of Mathematics and Computer Science– UT Faculty of Philosophy– UL Faculty of Humanities

• Key principles:– order of stimuli, gender, age, level of education

Raw Data• N = 238• 10, 15 … 1 rpm = 134• 10, 5 … 15 rpm = 104• Gender:

– Males: 63– Females: 175

• Age: group from 20-29 = 172• Education:

– Secondary school = 88– Bachelor degree = 80

• Country of origin: 30 countries (Estonia, Latvia, Syria, Israel, Australia, etc.)

Preliminary Processing of the Data

• Invalid responses:– Don’t see any lines;– Inconsistent responses (5 rpm = Y, 4 rpm = N, 3

rpm = Y);– Not observing the effect at 15 rpm or 10 rpm

• Normalisation of the responses:– The questions regarding the respondent– The questions regarding the perception of the

stimuli

Preliminary Processing of the Data

• Normalisation of the responses to the questions regarding the perception of the stimuli:– Normalised = 3– Not normalised = 24– ‘when vertical or horizontal, they [lines] appear

aligned; when at 45 or 135 degrees, the flashing line appears to lag slightly’

– ‘[the flashing line (or the first line!?)] sometimes lags a little behind, sometimes [is] aligned and sometimes [runs] ahead’

Data

• N = 175• By gender: M = 51, F = 124

N of respondents by gender0

20

40

60

80

100

120

140

MalesFemales

Data

Age

N of respondents by age0

20

40

60

80

100

120

140

Up to 1920-2930-39> 40

Data

Education

N of respondents by education0

10

20

30

40

50

60

70

80

Secondary SchoolBachelor degreeMaster's degreePhD

• Average threshold = 2,594 rpm• Bach = 1 rpm / 2 rpm

10

0.5

1

1.5

2

2.5

3

Average threshold for all respondents

Average threshold for all respondents

• M = 2,35• F = 2,69• Wilcoxon rank sum test: p = 0.064 • Not statistically significant, yet there is a trend

Male Female2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Average threshold by gender

Average Threshold

• Spearman correlation test: rho = -.177, p < 0.025

• Weak negative correlation

0-19 20-29 30-39 > 400

0.5

1

1.5

2

2.5

3

3.5

Average threshold by age

Average Threshold

• Kruskall Wallis test: p > 0.2• No effect

SS BA MA PHD0

0.5

1

1.5

2

2.5

3

Average threshold by education

Average Threshold

Conclusions

• Fairly large sample• All respondents: 2,594 rpm vs 1 rpm / 2 rpm• Gender: trend rather than effect• Age: weak negative correlation• Education: no effect• Limitations of the research• Further study: – Sample distribution by gender– Sample distribution by age

Thank you!