Multisensory perceptual awareness: Categorical or graded?
Jean-paul Noel, Nathan Faivre, Elisa Magosso, Olaf Blanke, David Alais, Mark Wallace
Cortex; a journal devoted to the study of the nervous system and behavior November 1, 2019 Peer reviewed DOI: 10.1016/j.cortex.2019.05.018 via PubMed
Summary
Reaction times to multisensory cues reported as unisensory are intermediate between those of fully aware and fully unaware cues, supporting graded forms of phenomenological consciousness. Artificial neural networks with feedback connectivity from multisensory to unisensory cortices produced the fastest responses for multisensory presentations with multisensory feedback and the slowest for those without. Psychophysical testing in 29 subjects each completing 10 hours of a multisensory cue-congruency task confirmed these intermediate reaction times, suggesting consciousness can be graded even in networks built on all-or-none models.
Study at a glance
| Design | experimental study with computational modeling and psychophysical testing |
|---|---|
| Sample size | 29 |
| Population | human subjects who completed a multisensory cue-congruency task |
| Key finding | Reaction times to multisensory cues reported as unisensory were intermediate between those of fully aware and fully unaware cues, supporting graded forms of phenomenal consciousness. |
Abstract
Neural evidence suggests that mechanisms associated with conscious access (i.e., the ability to report on a conscious state) are "all-or-none". Upon crossing some threshold, neural signals are globally broadcast throughout the brain and allow conscious reports. However, whether subjective experience (phenomenal consciousness) is categorical (i.e., transitioning abruptly from unconscious to conscious states) or graded (i.e., characterized by multiple intermediate states) remains an open question. To address this issue, we built a series of artificial neural networks containing distinct feedback connectivity from "multisensory" to "unisensory" cortices. In line with consciousness theories, we operationalized perceptual consciousness by the presence of feedback from higher-order nodes back to unisensory nodes which allow 'neural ignition' - a rapid, non-linear boost in response putatively leading to phenomenal consciousness. When simulating how these networks responded to unisensory and multisensory inputs, we found the fastest responses for multisensory presentations associated with multisensory feedback, and the slowest responses for multisensory presentations without feedback. Most interestingly, despite being built in line with "all-or-none" models of consciousness, multisensory stimuli associated with unisensory feedback (i.e., auditory or visual), and hence consistent with unisensory phenomenology according to theories of consciousness, generated intermediate reaction times. To extend these models to human perception and performance, we conducted extensive psychophysical testing in 29 subjects who each completed 10 h of a multisensory cue-congruency task. Consistent with the modeling results, we found that reaction times to multisensory cues reported as unisensory were intermediate between those of fully aware and fully unaware cues. These results support the existence of graded forms of phenomenological consciousness that can be instantiated by simple neural networks built in line with "all-or-none" models of consciousness.