Global visual perception
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Global visual perception. Velitchko Manahilov Uma Shahani Gael Gordon William Simpson. Outline. Reverse correlation analysis Classification image approach Perceptive fields for global motion in individuals with: - normal vision - amblyopia - dyslexia - persistent migraine aura

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Global visual perception

Global visual perception

Velitchko Manahilov

Uma Shahani

Gael Gordon

William Simpson


Outline

Outline

  • Reverse correlation analysis

  • Classification image approach

  • Perceptive fields for global motion in individuals with:

    - normal vision

    - amblyopia

    - dyslexia

    - persistent migraine aura

  • Conclusions


Global visual perception

Reverse correlation technique

Visual neurons are stimulated by noise images

and the spike output is cross-correlated with the input.


Global visual perception

Reverse correlation technique

Multifocal ERG & VEP


Global visual perception

What is a classification image?

The classification image shows

how the observer weights the information

in the image to reach a decision.


Global visual perception

Signal Detection Theory


Global visual perception

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<M>

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<H>

Criterion

Noise+Signal

response

Probability

MISS

HIT

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Internal response


Global visual perception

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<CR>

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<FA>

Criterion

Noise

response

Probability

Corr rej

False alarm

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2

4

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Internal response


Classification image

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<M>

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<H>

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<CR>

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<FA>

CI = <H> - <M> + <FA> - <CR> =

Classification image


Global visual perception

Manahilov & Simpson, VR, 2005.


Global visual perception

H-MF-C

Beard & Ahumada, JOSA, 1999.


Global visual perception

Gold, J.M., Murray, R.F., Bennett, P.J., & Sekuler, A.B. Current Biology 2000.


Global visual perception

Internal representation?

Observers were presented with 20,000 noise samples. They were told that the letter “S” was present on 50% of the trials. No more detail was given regarding the shape of the letter.

No signal was ever presented.

The classification image resembles the letter “S”.

Gosselin F. & Schyns P. Psychological Science, 14, 504-509, 2003.


Global visual perception

Global motion direction

Black discsdisc diameter - 20’speed - 5 deg/s4 frames of 50 msdisplay size - 10x10 deg


Perceptive field of ideal observer if s md i 0 right if s md i 0 left

Perceptive field of ideal observerif SMDi> 0 => Right if SMDi< 0 => Left


Global motion direction normal observers subj dd

Global motion directionnormal observersSubj. DD


Global motion direction normal observers subj jpk

Global motion directionnormal observersSubj. JPK


Global motion direction normal observers subj imk

Global motion directionnormal observersSubj. IMK


Global motion direction normal observers subj ls

Global motion directionnormal observersSubj. LS


Global motion direction normal observers average

Global motion directionnormal observersAverage


Amblyopia

Amblyopia

Amblyopia (lazy eye) is the loss or lack of development of central vision in one eye.

It is unrelated to any eye health problem and is not correctable with lenses.

It can result from a failure to use both eyes together.

Lazy eye is often associated with crossed-eyes or a large difference in the refractive errors between the two eyes.

It usually develops before the age of 6, and it does not affect side vision.


Global motion direction subj ch amblyopic eye fellow eye

Global motion directionSubj. CHAmblyopiceye Fellow eye


Global motion direction subj kh amblyopic eye fellow eye

Global motion directionSubj. KHAmblyopiceye Fellow eye


Global motion direction subj lw amblyopic eye fellow eye

Global motion directionSubj. LWAmblyopiceye Fellow eye


Global motion direction average amblyopic eye fellow eye

Global motion directionAverageAmblyopiceye Fellow eye


Global motion direction subj dd subj jpk va 6 18

Global motion direction Subj. DD Subj. JPK VA 6/18


Global motion direction

Global motion direction


Global motion direction1

Global motion direction


Global motion direction2

Global motion direction


Global motion direction3

Global motion direction


Dyslexia

Dyslexia

Developmental dyslexia is manifested as

a difficulty with reading given normal individual intelligence

that cannot be explained by other factors such as

sensory acuity, learning opportunities or brain injuries.


Global motion direction dyslexia

Global motion direction Dyslexia


Global motion direction dyslexia1

Global motion direction Dyslexia


Global motion direction dyslexia2

Average

Global motion direction Dyslexia


Persistent migraine aura

Persistent Migraine Aura

Persistent migraine aura is a rare but well documented complication of migraine.

Patients experience continuous aura lasting weeks or months.

These patients offer a unique opportunity to examine the migraineous brain during the aura phase of the attack.


Global motion direction persistent migraine aura

Global motion directionPersistent Migraine Aura


Global motion direction persistent migraine aura1

Global motion directionPersistent Migraine Aura


Global motion direction persistent migraine aura2

Average

Global motion directionPersistent Migraine Aura


Global visual perception

SUMMARY1. Classification image technique provides a new powerful tool for estimating the observers’ behavioural template for detecting objects.

2. Normal observers use localised perceptive fields when integrate global motion information. They extract motion information from central moving discs and suppress peripheral items.

3. The perceptive fields of individuals with amblyopia, dyslexia and persistent migraine aura are wider than the perceptive fields of normal observers.

4. The wider perceptive fields of these individuals may be related to reduced suppression of global (attentional) mechanisms which allows integrating motion information over a much larger field.

5. In the presence of environmental noise, these individuals may have deficits in exclusion of unwanted distractors.


Thank you

Thank you.


Perceptual noise exclusion deficits in dyslexia

Perceptual noise-exclusion deficits in dyslexia

Sperling et al., (2005). Nature Neuroscience, 8, 862-863.


Perceptual noise exclusion deficits in dyslexia1

Perceptual noise-exclusion deficits in dyslexia


Global motion direction persistent migraine aura3

Global motion direction Persistent Migraine Aura


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