Psychophysical evidence for impaired Magno, Parvo, and Konio-cellular pathways in dyslexic children

Abstract

Purpose:Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring luminance and color perception.Methods:Visual stimuli consisted of a series of natural images, divided into layers of luminance, red-green and blue-yellow, which probed magnocellular, parvocellular, and koniocellular pathways, respectively. Thirteen children with dyslexia and 13 sex- and age- matched controls performed three psychophysical tasks. In the first task, subjects were instructed to match the contrast of luminance (magno) and red-green (parvo) images to that of the blue-yellow (konio) images. In the second task, subjects detected the isoluminant point of red-green images to probe parvocellular pathway. In the third task, temporal processing was assessed by measuring reaction time and percentage of correct responses in an identification task using four categories of images, activating all three pathways.Results:The dyslexic group had significantly elevated luminance and color contrast thresholds and higher isoluminant point ratio in comparison to the control group. Furthermore, they had significantly less correct responses than the control group for the blue-yellow images.Conclusion:We may suggest that dyslexic subjects might suffer from both magnocellular and parvocellular deficits. Moreover, our results show partial impairment of the koniocellular pathway. Thus, dyslexia might be associated with deficits in all three visual pathways.

Comparison of color discrimination in chronic heavy smokers and healthy subjects

“…As stated, this result does not support the idea of channel selectivity. However, we base our rational on the existence of diffuse processing impairment, which may include magno- and parvocellular pathways 28 .…”

“…However, our tests used pseudoisochromatic stimuli. Thus, color discrimination may have occurred through dorsal and ventral stream 28 . Too soon to conclude anything, but there may be nAChRs in both dorsal and ventral stream 47 and both streams may suffer from the action of neurotrasmission hypofunction, affecting directly visual processing 39 – 41 , 43 .…”

Colour discrimination thresholds in type 1 Bipolar Disorder: a pilot study

“…Furthermore, the use of a psychophysical method that has been widely used over the years tries to eliminate the relation between the participant’s sensitivity and possible bias 43 , 44 . Thus, the use of the tests we employed (mainly CCT subtests), under these conditions, sought to reduce the impact of inter- and intra-individual differences.…”

“…Our findings suggest that one or more of these CV systems may have been dysfunctional because we observed diffuse impairments for CCIs and also CCT Trivector and Ellipse. The use of these measurements may suggest the existence of possible visual pathways impairments 43 , 46 . Nonetheless, we cannot make definitive conclusions based only on the use of visual psychophysics, although these measures are known to be very reliable and can detect even subtle losses in CV.…”

Tobacco Use Decreases Visual Sensitivity in Schizophrenia

“…The CSF is one of the main measures to verify the response of the visual system in healthy, preclinical, and clinical populations under scotopic, mesopic, and photopic luminance conditions. The CSF also allows observations of activity of the magnocellular, parvocellular, and koniocellular visual pathways ( Xu et al, 2001 ; Ahmadi et al, 2015 ; Skottun, 2015 ). It also allows determination of the response of the visual system in processing rough attributes and fine details of objects that are modulated by low, medium, and high spatial frequency bands ( DeValois and DeValois, 1990 ; Cornsweet, 2012 ).…”