Bringing action into the picture. How action influences visual awareness
Recent studies suggest that action may influence visual awareness. I will report the results of the project investigating the relation between action and awareness on behavioural and neuronal level. The studies applied perceptual discrimination task. In E1, presentation of the stimulus was immediately followed by a cue requiring a motor response that was irrelevant to the task but could be the same, opposite, or neutral to the correct response to the stimulus. After responding to the cue, participants rated their stimulus awareness using the Perceptual Awareness Scale (PAS), and then carried out their discrimination response. Participants reported a higher level of stimulus awareness after carrying out responses that were either congruent or incongruent with the response required by the stimulus, compared to the neutral condition. In E2, we used a single-pulse Transcranial Magnetic Stimulation (sp-TMS) to excite primary motor cortex (M1). Delivering sp-TMS to M1 resulted in higher average PAS ratings as compared to the control stimulation condition, but only in trials where stimulation was congruent with the following identification task response. We concurrently measured motor evoked potentials (MEPs) and showed that they can serve as an indirect measure of both perceptual and non-perceptual evidence accumulated for visual awareness ratings. Based on the results of our studies as well as other experiments reported in the literature, we argue that activity in motor cortex influences visual awareness of the participants. We also discuss the possible mechanisms that underlie these influences on both the cognitive and the neural levels. We propose that action may affect visual awareness because (1) it serves as additional information in the process of evidence accumulation; (2) it restricts the number of alternatives in the decisional process; (3) it enables error detection and performance monitoring; and/or (4) it triggers attentional mechanisms that modify stimulus perception. We also discuss the possible neuronal mechanisms of the aforementioned effects, including feedback-dependent prefrontal cortex modulation of the activity of visual areas, error-based modulation, interhemispheric inhibition of motor cortices, and attentional modulation of visual cortex activity triggered by motor processing. We also concluded that interactions between action and visibility judgments allows us to better understand the mechanisms of visual awareness.
