Cognition does not automatically influence perception: Evidence from neural encoding of colours belonging to different categories

The firmest evidence in favour of models that posit early high-level influences of cognition on perception comes from electroencephalography (EEG). Enhanced early, pre-attentive processing of light and dark blue feature changes compared to light and dark green changes was reported in Greek speakers, who have two basic terms for blue (ghalazio/ble). In the present three-experiment study, we systematically re-evaluate this evidence and test an alternative model that the early difference waves in the human EEG instead mainly reflect contrast adaptation phenomena. We use the same classical oddball paradigm presenting alternating standards and deviants that systematically differ in colour and/or luminance and chromatic contrast. We then calculate the visual mismatch negativity (vMMN), a putative index of pre-attentive feature change processing and predictive coding derived from EEG data, by subtracting the activity elicited by standards from that elicited by task-irrelevant deviants. Our experiments demonstrate the following: 1) vMMN is driven by contrast adaptation, being observable only in the presence of contrast differences between the stimuli and not reliably observed for categorically different hues equated in contrast; 2) there is no reliable difference between green- and blue-related difference waves in speakers (Russian) with two basic blue colour categories, the difference waves, again, being driven by contrast rather than their categorical content. Our findings are highly significant for the debate concerning the interface between perception and cognition, as the absence of early categorical effects speaks against models that predict Whorfian-type pre-attentive cognitive influences on perception. Significance statementThe Whorfian hypothesis posits that basic language categories alter ones perception of the world in a fundamental manner. Some of the most compelling evidence in favour of this hypothesis came from electrophysiological responses that indicated early differences between speakers of languages with different number of basic colour categories. The brain response taken as an indicator of these differences was considered to be a robust marker of early, pre-attentive processing and predictive coding. In the current multi-experiment study, we present evidence that early electrophysiological differences to colour reflect signatures of hue, saturation and luminance contrast and adaptation to this contrast, rather than of linguistic categories. This means that evidence in favour of early, pre-attentive categorical colour perception has been significantly eroded.