Task Difficulty Regulates the Attentional Gain Modulations in Human Early Visual Cortex

Task difficulty is thought to influence perceptual performance by mediating the gain of neural responses in early sensory areas. In support of this idea, a study in non-human primates found that increasing task difficulty enhanced the gain of the single-unit activity of neurons in the early visual cortex. However, other research groups have reported either null or even reversed effects of task difficulty on gain modulations in single-unit activity. Derived from Yerkes-Dodson's Law, it is possible that this discrepancy emerged from an interaction between task difficulty and attentional gain modulations that occurs in a non-linear inverted-U fashion. Here, we used EEG to measure modulations in visual cortex of male and female human participants performing an attention cueing task where we systematically manipulated task difficulty across blocks of trials. Consistent with Yerkes-Dodson’s law, our behavioral and neural data implicate an inverted-U relationship between task difficulty and selective attention. Specifically, when task difficulty was adjusted to an intermediate level (~76% accuracy), a focused-attention cue led to larger response gain in both neural and behavioral data compared to when behavioral tasks were harder (~65% accuracy) or easier (~91% accuracy). Moreover, difficulty-related changes in response gain modulations in early visual cortex positively correlated with those predicted by quantitative modelling of the behavioral data. Taken together, these findings suggest that task difficulty mediates attention-related changes in perceptual performance via different modulations of attentional gain in human visual cortex. [Funding was provided by NEI R01 and a James S. McDonnell Foundation award to John T Serences. This project was also funded by the National Research Council of Thailand grant (fiscal year 2021), the Thailand Science Research and Innovation Basic Research grant (fiscal year 2021 under project numbers 64A306000016 and fiscal year 2020 under project number 62W1501), the Asahi Glass Foundation grant, the research grant from the Research & Innovation for Sustainability Center, Magnolia Quality Development Corporation Limited, Thailand, the KMUTT Partnering initiative grant (fiscal year 2021), and the startup fund for junior researchers at King Mongkut’s University of Technology Thonburi (KMUTT), and the KMUTT’s Frontier Research Unit Grant for Neuroscience Center for Research and Innovation to Sirawaj Itthipuripat.]