visual processing in fingerprint experts and novices tom busey indiana university, bloomington john...
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Visual Processing in Fingerprint Experts and Novices
Tom BuseyIndiana University, Bloomington
John VanderkolkIndiana State Police, Fort Wayne
Expertise with fingerprint examiners was tested in behavioral and EEG studies. Experts show greater tolerance for noise, are unaffected by longer memory delays, and show evidence of configural processing. This last finding was confirmed in an EEG study where experts show a reliable delay of the N170 component when fingerprints were inverted, while novices did not. Configural processing may be one element that underlies perceptual expertise.
www.indiana.edu/~busey/
Testing Fingerprint Expertise:X-AB Sequential Matching Task
Study Image1 Second
Mask 200 or 5200Milliseconds
Test ImagesUntil Response
example stimulus pairs:
Reduce Matching based on Low-Level Features
• Overall Brightness change
• Study image is rotated up to 90° in either direction
• Two image manipulations designed to simulate latent prints– Added noise– Partial masking
Partial Masking
Semi-TransparentMasks
Fingerprint Partially MaskedFingerprints
Logical Combination
Recovers OriginalFingerprint
orig
inal
inve
rse
Image Degradations at Test
Clear FragmentsPartially-Masked Fragments
Partially-Masked FragmentsPresented in NoiseFragmentsPresented in Noise
Partial Masking
Semi-TransparentMasks
Fingerprint Partially MaskedFingerprints
SummationRecovers Original
Fingerprint
orig
inal
inve
rse
0.5
0.6
0.7
0.8
0.9
1.0
Full Image Partial Image
Experts- Short Delay
No NoiseNoise Added
Percent Correct
Image Type
0.5
0.6
0.7
0.8
0.9
1.0
Full Image Partial Image
Experts- Long Delay
No NoiseNoise Added
Percent Correct
Image Type
0.5
0.6
0.7
0.8
0.9
1.0
Full Image Partial Image
Novices- Short Delay
No NoiseNoise Added
Percent Correct
Image Type
0.5
0.6
0.7
0.8
0.9
1.0
Full Image Partial Image
Novices- Long Delay
No NoiseNoise Added
Percent Correct
Image Type
Behavioral Data
Full Images Partial Images
Full Images in Noise
Partial Images in Noise
Experts: No effect of delay, interaction between noise and partial masking.
Evidence for Configural ProcessingFull Image (Both Halves) Partial Image (One Half)
Question: What is the relation between db and do?if db = do : One half doesn't influence information acquired from other halfif db < do : Get less information from one half when second is presentif db > do : Get more information from one half when second is present
(consistent with configural or gestalt processing)
info from first half?
no(1-db)
yes(db)
no(1-db)
yes(db)
info from second half?
no(1-g)
yes(g)
info from guessing?
Correct Decision Wrong Decision
no(1-do)
yes(do)
info from first half?
no(1-g)
yes(g)
info from guessing?
Correct Decision Wrong Decision
Evidence for Configural Processing: Multinomial Modeling
To test for configural processing, we can use the accuracy rate in the partial image condition to make a prediction for the full image condition, assuming no configural processing. If performance in the full image condition exceeds the prediction, we have evidence that is consistent with configural processing.
Evidence for Configural Processing: Multinomial Modeling
To test for configural processing, we can use the accuracy rate in the partial image condition to make a prediction for the full image condition, assuming no configural processing. If performance in the full image condition exceeds the prediction, we have evidence that is consistent with configural processing.
Experts in noise: We predict performance in the full image condition to be about 75% correct. Instead it is around 90%. Experts are doing better with the whole image than we predict they would do based on partial-image performance. This is configural processing at work.
Configural Processing in Faces: The ‘Thatcher Illusion’
(Thomson, 1980)
Features are perceived
individually, image looks ok.
Features are perceived in
context, image looks grotesque.
EEG Recording Basics
• Record from the surface of the scalp
• Amplify 20,000 times• Electrical signals are
related to neuronal firing, mainly in post-synaptic potentials in cortex.
• Very small signals, very noisy data.
EEG and Configural ProcessingFaces produce a strong component
over the right hemisphere at about 170 ms after stimulus onset, which is called the N170. Inverted faces cause a delay of 10-20 ms in the N170.
Trained objects (Greebles) show a delay in the N170 component with inversion, but only in the left hemisphere (channel T5).
Data from Rossion, Gauthier, Goffaux, Tarr & Crommelinck (2002)
Data from Rossion, Gauthier, Tarr, Despland, Bruyer, Linotte & Crommelinck (2000)
Coupled with behavioral data suggesting configural processing with faces, an advanced N170 to an upright stimulus suggests that the N170 latency differences indicate configural processing.
An Obvious Experiment:
Show upright and inverted fingerprints to Fingerprint examiners and novices. If experts process fingerprints configurally, we should see a delayed N170 to inverted fingerprints.
Also test faces to replicate the face inversion effect in our subjects. Test both identification and categorization tasks.
0 100 200 300 400 500
-1.3
9.3
AllExperts Identification Task
Expert Data- Identification TaskA
mpl
itud
e (µ
V)
Time (ms)
Upright FingerprintInverted FingerprintUpright FaceInverted Face
Delayed
Delayed
Experts: delayed N170 withinverted fingerprints and invertedfaces.
Electrode T6
0 100 200 300 400 500
-2.9
17
AllNovices Identification Task
Novice Data- Identification Task
Upright FingerprintInverted FingerprintUpright FaceInverted Face
Am
plit
ude
(µV
)
Time (ms)
Delayed
No Delay
Novices: no delayed N170 withinverted fingerprints, but see with faces.
Electrode T6
0 100 200 300 400 500
-3.3
5.6
AllExperts Categorization Task
Expert Data- Categorization TaskA
mpl
itud
e (µ
V)
Time (ms)
Upright FingerprintInverted FingerprintUpright FaceInverted Face
Delayed
Delayed
Experts: delayed N170 withinverted fingerprints and invertedfaces.
Electrode T6
0 100 200 300 400 500
-2.4
13
AllNovices Categorization Task
Novice Data- Categorization Task
Upright FingerprintInverted FingerprintUpright FaceInverted Face
Am
plit
ude
(µV
)
Time (ms)
Delayed
No Delay
Novices: no delayed N170 withinverted fingerprints, but see with faces.
Electrode T6
Summary and ConclusionsFingerprint experts demonstrate strong performance in an X-AB matching task, robustness to noise and evidence for configural processing when stimuli are presented in noise. This latter finding was confirmed using upright and inverted fingerprints in an EEG experiment. Experts showed a delayed N170 component for inverted fingerprints in the same channel that they show a delayed N170 for inverted faces. Thus they appear to be processing upright fingerprints in part using configural or holistic processing, which stresses relational information and implies dependencies between individual features. In the case of fingerprints, this may come from idiosyncratic feature elements instead of well-defined features such as eyes and mouths.
www.indiana.edu/~busey/