Language suppression effects on the categorical perception of colour as evidenced through ERPs.

It is unclear how language influences colour perception so as to lead to the categorical perception of colour. This is particularly true when considering visual tasks that involve minimal memory requirements. In the present experiment we investigated this question by employing a "same-different" judgment task in which participants were asked to compare the colours of two presented visual features (a square and its surrounding frame), presented to the left visual field (LVF) or the right visual field (RVF), while event-related potentials (ERPs) were recorded. The "different" colour trials were of two types, including those consisting of within-category differences (e.g. two different shades of blue) and those consisting of between-category differences (i.e. blue vs. green), with matching hue differences for within-category comparisons and between-category comparisons. The ERP results show that, over the midline fronto-central scalp region, responses to the within-category stimuli presented in the RVF demonstrated a more negative N2 component (260-310 ms post-stimulus) than either the responses to the between-category stimuli in the RVF, the between-category stimulus in the LVF, or the within-category stimulus in the LVF. Further, the responses for the within-category stimulus in the RVF resulted in a P3 component with a longer latency than that observed for the other three conditions. The results observed in this rapid colour discrimination task suggest that the categorical perception of colour stimuli presented in the RVF may result from an effect of language-related processes suppressing the capacity to discriminate two shades of colour within the same colour category.