Very Early Responses to Colour Stimuli Detected in Prestriate Visual Cortex by Magnetoencephalography (MEG)

Abstract

Key points summary・ We measured visual evoked responses to colour stimuli using magnetoencephalography.・ An early response was identified, at around 30 ms after stimulation.・ The sources of the response were estimated to be in prestriate cortex.・ Colour signals thus appear to evoke very early cortical responses, just like form and motion signals. 3 AbstractPrevious studies with the visual motion and form systems show that visual stimuli belonging to these categories trigger much earlier latency responses from the visual cortex than previously supposed and that the source of the earliest signals can be located in either the prestriate cortex or in both the striate (V1) and prestriate cortex. This is consistent with the known anatomical connections since, in addition to the classical retino-geniculo-striate cortex input, there are direct anatomical inputs from both the lateral geniculate nucleus and the pulvinar that reach the prestriate visual cortex without passing through V1. In pursuing our studies, we thought it especially interesting to study another cardinal visual attribute, namely colour, to learn whether colour stimuli also provoke very early responses, at less than 50 ms, from visual cortex. To address the question, we asked participants to view stimuli that changed in colour and used magneto-encephalography to detect very early responses (< 50 ms) in the occipital visual cortex. Our results show that coloured stimuli also provoke an early cortical response (M30), with an average peak time at 30.8 ms, thus bringing the colour system into line with the visual motion and form systems. We conclude that colour signals reach visual cortex, including prestriate visual cortex, earlier than previously supposed. 4

“Multiplexing” cells of the visual cortex and the timing enigma of the binding problem

“…This is even in spite of the fact that signals may indeed be processed successively at a non‐conscious level (Herzog, Kammer, & Scharnowski, 2016; Poncelet & Giersch, 2015), which of course fortifies the belief in asynchronous processing; in the experiments that reveal the perceptual asynchrony in the micro‐perceptive world, subjects attend to and report the stimuli (and hence are conscious of them). The time scales I give here are only approximate; visual signals reach the visual brain (both V1 and the specialized visual areas outside it) from the lateral geniculate nucleus (LGN) much earlier than previously thought, at periods of about 28–40 ms after the appearance of the visual stimulus (Beckers & Zeki, 1995; ffytche, Guy, & Zeki 1995; Shigihara, Hoshi, & Zeki, 2017; Shigihara & Zeki, 2013, 2014). The temporal dynamics of what happens after this initial period is not clear.…”