Dissociable neural mechanisms underlying selective attention, perceptual difficulty, and global cognitive factors

Selective attention and perceptual demand play a critical role in shaping the efficiency and speed
of early sensory and decision processes. Directing attention enhances processing of the attended stimulus,
while increased perceptual difficulty can amplify the effects of selective attention on visual cortical
processing. However, when a perceptual task becomes excessively challenging, the effects of selective
attention may diminish. Although recent studies have systematically investigated the effects of selective
attention and perceptual difficulty, the potentially distinct neural dynamics that underlie these processes
and their relationship with global cognitive factors such as stress and arousal remain poorly understood.
To address this gap, our study aimed to uncover the distinct neural processes associated with selective
attention and perceptual difficulty, and examine how they differ from global cognitive factors. Using
EEG, we recorded brain activity while participants performed a visual discrimination task. We
manipulated selective attention with spatial cues and perceptual difficulty by adjusting contrast
increments of visual stimuli. Additionally, we examined the effects of general task difficulty on medium-
difficulty trials interleaved between easy and difficult blocks. Our findings revealed that subjective stress
and arousal levels were significantly higher during difficult blocks compared to easy blocks. Consistent
with past studies, we observed that attentional modulations of early visually evoked activity (P1
component) and decision-related positive deflection (P3 component) were attenuated under high
perceptual difficulty. However, global task difficulty modulated behavioral performance without affecting
these neural responses. Notably, alterations in global task difficulty did influence oscillatory events in
alpha and beta band frequencies, which are thought to reflect overall task engagement and arousal states
in the cortex. Taken together, our study sheds light on the distinct influences of selective attention,
perceptual difficulty, and global cognitive factors on early sensory and decision-making processes.