Previous studies have found that spatial processing in children and adults with Down syndrome is different in comparison to the normal population. Some previous studies have also found that there is a high prevalence of colour vision deficiencies in people with Down syndrome. The aim of the present study was to use an objective test, the transient visual evoked potential (VEP), to assess achromatic and chromatic visual processing in adults with Down syndrome. Achromatic VEPs were recorded in

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... ponse to black-white stimuli presented in pattern reversal mode. Chromatic VEPs were recorded in response to two types of colour pattern, presented in pattern onset-offset mode. The two colour types were intended to preferentially stimulate the two principal chromatic pathways of the visual system, the 'red-green' and 'blue-yellow' colour-opponent pathways. These stimuli are here termed the 'LM' and 'S-(L+M) stimuli, respectively, reflecting the cone types that input to the pathways they are intended to stimulate. Each subject also completed two subjective colour vision tests, the Colour Vision Test Made Easy (CVTME) and the City University Colour Vision Test (CUT). Morphology of the achromatic and chromatic VEPs was found to differ between the group with Down syndrome and an age-matched control group. The latency of the P100 component of the achromatic VEP was found to be significantly later in the group with Down syndrome compared to the control group (the N75 latency was earlier in the group with Down syndrome, but not significantly so). The group-averaged peak-to-peak amplitude of the achromatic VEP was significantly lower in the group with Down syndrome compared to the control group. The major positive component of the VEP in response to the L-M stimulus was of significantly longer latency compared to that of the control group. The major negative component and the peak-to-peak amplitude of this response were not significantly different between the groups. For the response to S-(L+M) stimuli, the latency of the major n [...]