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/

How Do Experts Make Identifications?

Eas

y M

atch

Har

d M

atch

An Experiment

Study Fragment

About a second

Mask

Either about a second or 3 seconds

Test Images

Until Response

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

Added Noise

Partial Masking

Partial Masking

Semi-TransparentMasks

Fingerprint Partially MaskedFingerprints

Logical Combination

Recovers OriginalFingerprint

orig

inal

inve

rse

Includes combinations:

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 Recording Basics• Average over lots of trials (200 trials per condition)

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/