Isolating the koniocellular contribution to aversive learning in human visual cortex

Prior work using steady-state visual evoked potentials (ssVEPs) to measure visuocortical activity related to the koniocellular visual pathway has shown a unique pattern of enhanced ssVEP amplitude. Specifically, the ssVEP tends to be heightened when viewing tritan stimuli compared to luminance stimuli. The tritanopic approach (Cavanagh et al., 1992) used to isolate the koniocellular pathway via activation of S-cones is a robust technique enabling the comparison of tritanopic and luminance conditions. It remains unclear how characteristics of tritan stimuli, like conditioned aversive valence, modulate this effect. To address this question, a series of experiments explored the impact of aversive conditioning on visuocortical responses to tritan and luminance stimuli, using ssVEP frequency tagging. In experiments 1 and 2, participants (N=27) completed a differential classical conditioning task with habituation, acquisition, and extinction phases. Each trial included a pre-stimulus adaptor period, containing only a central fixation point over a uniform yellow background (tritan stimulus) or a uniform black background (luminance stimulus). Following the adaptor, a random dot kinematogram (RDK)—white dots superimposed on adaptor—flickered at driving frequencies of 14 Hz (N=13) and 17.14 Hz (N=14). Moreover, the RDK moved in one of two directions (135 or 225 degrees) that signaled the presence (CS+) or absence (CS-) of threat (92 dB white noise burst). It was observed that tritan stimuli (CS+ and CS-) drove stronger ssVEP signals than luminance stimuli. This main effect increased in the acquisition phase, consistent with arousal-based modulation of the koniocellular pathway. Furthermore, luminance and tritan CS+ activity showed the expected selective amplitude enhancement late in the viewing epoch. A third ongoing study aims to replicate these effects with oriented gratings using the same manipulations. Results are consistent with findings showing heightened ssVEP for tritan stimuli and with theoretical notions emphasizing the role of the koniocellular pathway in processing motivational relevance.