Global visual perception Velitchko Manahilov Uma Shahani Gael
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 Signal Signal + + Noise Noise + + Signal + Noise + Signal + Noise + + +
Criterion response Probability Noise+Signal MISS 0 2 HIT 4 6 Internal response 8 10 Signal
Signal + + Noise Noise + + Signal + Noise + Signal + Noise + + + Criterion response Probability
CI = - + - = Manahilov & Simpson, VR, 2005. H-M F-C Beard & Ahumada, JOSA, 1999. Gold, J.M., Murray, R.F., Bennett, P.J., & Sekuler, A.B. Current Biology 2000. 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. Gosselin F. & Schyns P. Psychological Science, 14, 504-509, 2003. The classification image resembles the letter S. Global motion direction Black discs disc diameter - 20 speed - 5 deg/s
4 frames of 50 ms display size - 10x10 deg Signal Right Left Right RR (NRR) LR (NLR) Left RL (NRL) LL (NLL) Response 1 Classifica tion image N RR N RR 1 ( RR
) i N LR i 1 N LR 1 ( LR ) i i 1 N LL NLL 1 ( LL ) i N RL i 1
N RL ( RL ) i i 1 Perceptive field of ideal observer if MDi> 0 => Right if MDi< 0 => Left Global motion direction normal observers Subj. DD (a) Classification Image (b) Classification Image p<0.001 20 Amplitude Amplitude 20 10 0
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 (a) Classification Image (b) Classification Image p<0.001 (a) Classification Image -10 10 10 0 Distance (deg) -10 -10 0
0 Distance (deg) 5 Global motion direction Average Amblyopic eye Fellow eye Global motion direction Subj. DD Subj. JPK VA 6/18 Proportion correct responses Global motion direction 1 CH 0.9 0.8 0.7 AE 9x9
0.6 0.5 0 5 10 15 Relative motion direction (deg) 20 Proportion correct responses Global motion direction 1 CH 0.9 0.8 0.7 FE 9x9 0.6
AE 9x9 0.5 0 5 10 15 Relative motion direction (deg) 20 Proportion correct responses Global motion direction 1 CH 0.9 0.8 0.7 FE 9x9
0.6 AE 9x9 FE 3x3 0.5 0 5 10 15 Relative motion direction (deg) 20 Proportion correct responses Global motion direction 1 CH 0.9 0.8 FE 9x9
AE 9x9 FE 3x3 AE 3x3 0.7 0.6 0.5 0 5 10 15 Relative motion direction (deg) 20 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 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 Global motion direction Persistent Migraine Aura 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. 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. Perceptual noise-exclusion deficits in dyslexia Sperling et al., (2005). Nature Neuroscience, 8, 862-863. Perceptual noise-exclusion deficits in dyslexia Contrast threshold (%) Non-dyslexics Dyslexics 16 1.2 8 0.9 4 0.6 2 0.3 1 0.0
No Noise High Noise Global motion direction Persistent Migraine Aura Efficiency d real 2 d ideal 2 0.25 Efficiency 0.2 0.15 0.1 0.05 0 Control (n=7) Persistent Aura (n=5)
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