On the cyclic nature of perception in vision versus audition

Abstract

Does our perceptual awareness consist of a continuous stream, or a discrete sequence of perceptual cycles, possibly associated with the rhythmic structure of brain activity? This has been a long-standing question in neuroscience. We review recent psychophysical and electrophysiological studies indicating that part of our visual awareness proceeds in approximately 7–13 Hz cycles rather than continuously. On the other hand, experimental attempts at applying similar tools to demonstrate the discreteness of auditory awareness have been largely unsuccessful. We argue and demonstrate experimentally that visual and auditory perception are not equally affected by temporal subsampling of their respective input streams: video sequences remain intelligible at sampling rates of two to three frames per second, whereas audio inputs lose their fine temporal structure, and thus all significance, below 20–30 samples per second. This does not mean, however, that our auditory perception must proceed continuously. Instead, we propose that audition could still involve perceptual cycles, but the periodic sampling should happen only after the stage of auditory feature extraction. In addition, although visual perceptual cycles can follow one another at a spontaneous pace largely independent of the visual input, auditory cycles may need to sample the input stream more flexibly, by adapting to the temporal structure of the auditory inputs.

Visual cortex entrains to sign language

“…We consider two hypotheses. First, flexible entrainment to quasiperiodic rhythms may be specific to auditory perception (6); in visual perception, by contrast, cortical oscillations in the alpha band (8)(9)(10)(11)(12) Hz) may phase-lock only to consistent stimulus rhythms, without adjusting to variable stimulus rhythms (16). Second, lowfrequency cortical entrainment may be a general-purpose neural mechanism that helps optimize perception to time-varying stimuli regardless of the perceptual modality.…”

Perceptual awareness and its neural basis: bridging experimental and theoretical paradigms

“…Several of the contributed articles report new experimental findings supporting theoretical claims, hypotheses and predictions [17,38,47,56,59]. Others emphasize review and theoretical aspects; however, they are systematically and critically related to relevant empirical findings with different experimental paradigms.…”

“…Both these aspects are considered in depth, together with relevant foundational (see in particular [52]) and methodological (see in particular [92]) problems. Insights with patient studies are also considered and bridged with evidence from psychophysical experiments [52] In addition to a number of articles on visual awareness, articles in this Theme Issue cover auditory perception [56], multisensory perception [92] and the role of bodily signals for perceptual awareness [93].…”

“…Fast and slow brain oscillations and processing steps as related to perceptual awareness, attentional and conscious processes are considered across several articles in the Theme Issue [25,32,56]. Some of the contributed articles with a neuroscientific focus emphasize (visual) cortical systems (pathways), with a revised functional perspective [14], whereas others, with a neurodynamic emphasis [25,32], also refer to interactions between visual cortex and the thalamus, with special reference to the pulvinar, a collection of higher order associative thalamic nuclei, of which the functional importance for perceptual awareness and attention is increasingly recognized.…”

“…It comprises contributions focused on advances about more 'classical' aspects of perceptual awareness, such as visual masking [14], binocular rivalry [29,32], the roles of attention [25,38] and conscious access, such as inattentional blindness and attentional blink [25], and others stressing new interesting directions to explore, such as the cyclic (discrete) nature of perception in vision versus audition [56], multisensory awareness [92] and the role of internal body representations for enabling subjectivity in perceptual experiences [93]. Visual search findings and theories are also considered [25].…”