The sounds we hear


A paper in Nature Neuroscience, ‘Predicting visual stimuli on the basis of activity in auditory cortices’, by Meyer, Kaplan, Essex, Webber, Damasio, Damasio, gives a picture of the role of the earliest sensory cortex in conscious experience. If a perception is in consciousness then it can be found in the ealy sensory cortex even if it is not part of the current sensory input.

Using multivariate pattern analysis of functional magnetic resonance imaging data, we found that the subjective experience of sound, in the absence of auditory stimulation, was associated with content-specific activity in early auditory cortices in humans. As subjects viewed sound-implying, but silent, visual stimuli, activity in auditory cortex differentiated among sounds related to various animals, musical instruments and objects. These results support the idea that early sensory cortex activity reflects perceptual experience, rather than sensory stimulation alone.

They discuss the evidence that this also happens in sight and touch.

There is growing evidence for an involvement of early sensory cortices in the conscious experience of sight and touch. For example, in perceptual illusions, activity in primary visual and somatosensory cortices has been shown to correspond more closely to the subjects’ visual or haptic experience than to the physical properties of the stimuli presented. Furthermore, when subjects imagine visual objects in the complete absence of perceptual input, primary visual cortices are activated and appear to specifically represent the contents of the subjects’ visual experience. Activity in primary visual cortices has also been shown to correlate with stimuli that are kept active in working memory. Although previous studies have established that early auditory cortices can be activated during auditory imagery, auditory hallucinations and the perception of implied sound, the content specificity of such activations has not yet been demonstrated. Our findings suggest that, just as in the visual and somatosensory modalities, activity at the earliest stages of cortical auditory processing correlates specifically with the experience of sound reported by the subjects, rather than with the actual auditory environment alone, as the latter was entirely silent during the presentation of the video clips.

So does this mean that we are closer to qualia? No matter why a sight, touch or sound is in consciousness (current perception, imagining, memory, hallucination) its footprint is found in the early sensory cortex where we would expect only signals just starting their perceptual journey.

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