Global visual perception Velitchko Manahilov Uma Shahani Gael Gordon William Simpson.

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Presentation transcript:

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   Conclusions

Reverse correlation technique Visual neurons are stimulated by noise images and the spike output is cross-correlated with the input.

Reverse correlation technique Multifocal ERG & VEP

What is a classification image? The classification image shows how the observer weights the information in the image to reach a decision.

Signal Detection Theory

Noise+Signal Internal response Probability MISSHIT Criterion response + +

Noise Internal response Probability Corr rej False alarm Criterion response + +

Classification image CI = =

Manahilov & Simpson, VR, 2005.

Beard & Ahumada, JOSA, H-M F-C

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

Gosselin F. & Schyns P. Psychological Science, 14, , 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”.

Black discs disc diameter - 20’ speed - 5 deg/s 4 frames of 50 ms display size - 10x10 deg Global motion direction

SignalResponseRightLeft Right RR (N RR ) LR (N LR ) Left RL (N RL ) LL (N LL )

Perceptive field of ideal observer if  MD i > 0 => Right if  MD i Left

Global motion direction normal observers Subj. DD

Global motion direction normal observers Subj. JPK

Global motion direction normal observers Subj. IMK

Global motion direction normal observers Subj. LS

Global motion direction normal observers Average

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 direction Subj. KH Amblyopic eye Fellow eye

Global motion direction Subj. LW Amblyopic eye Fellow eye

Global motion direction Average Amblyopic eye Fellow eye

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

Global motion direction

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

Average

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

Average

SUMMARY 1. Classification image technique provides a new powerful tool for estimating the observers’ behavioural template for detecting objects. 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. 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. 5. In the presence of environmental noise, these individuals may have deficits in exclusion of unwanted distractors.

Thank you.

Perceptual noise-exclusion deficits in dyslexia Sperling et al., (2005). Nature Neuroscience, 8,

Perceptual noise-exclusion deficits in dyslexia

Global motion direction Persistent Migraine Aura