Binaural summation of amplitude modulation involves weak interaural suppression

Abstract

The brain combines sounds from the two ears, but what is the algorithm used to achieve this summation of signals? Here we combine psychophysical amplitude modulation discrimination and steady-state electroencephalography (EEG) data to investigate the architecture of binaural combination for amplitude-modulated tones. Discrimination thresholds followed a 'dipper' shaped function of pedestal modulation depth, and were consistently lower for binaural than monaural presentation of modulated tones. The EEG responses were greater for binaural than monaural presentation of modulated tones, and when a masker was presented to one ear, it produced only weak suppression of the response to a signal presented to the other ear. Both data sets were well-fit by a computational model originally derived for visual signal combination, but with suppression between the two channels (ears) being much weaker than in binocular vision. We suggest that the distinct ecological constraints on vision and hearing can explain this difference, if it is assumed that the brain avoids over-representing sensory signals originating from a single object. These findings position our understanding of binaural summation in a broader context of work on sensory signal combination in the brain, and delineate the similarities and differences between vision and hearing.

Dichotic integration of acoustic-phonetic information: Competition from extraneous formants increases the effect of second-formant attenuation on intelligibility

“…Regarding the question of whether both these processes are relevant to the integration of acoustic-phonetic information across ears, it is perhaps worth noting that a computational model of vision incorporating interocular suppression (inhibition) prior to binocular integration (Baker et al, 2007) has been very successful in accounting for the results of psychophysical binocular contrast discrimination and matching experiments. Indeed, this approach has recently been extended successfully to modeling thresholds for amplitudemodulation depth discrimination for various binaural stimulus configurations on the assumption that interaural inhibition is weaker than interocular inhibition (Baker et al, 2018). Although there are clearly limits to the analogy that can be drawn with combining suprathreshold sources of acoustic-phonetic information-e.g., F2 and F2C occupy the same frequency region but their trajectories are very different-this general approach may offer a way of accounting for results like those reported here.…”

Effects of spatial attention and limb position on the cortical interaction of bilateral noxious inputs

“…In the present study, the lack of effect of spatial attention on the increase of pain-related EEG responses for bilateral compared with unilateral stimulation may reflect an involuntary capture of attention by the concurrent stimulus, consistent with the representation of a more salient physical threat, as mentioned above. In other sensory modalities, including the visual system, it is only beneficial to integrate the information from two concurrent stimuli when both signals are very weak (around the detection threshold) and the signalto-noise ratio is low (Baker et al, 2020). In the case of noxious stimuli used in the present study, they are salient and clearly above threshold, so it is possible that no further effect could be observed by manipulating spatial attention.…”

Different rules for binocular combination of luminance flicker in cortical and subcortical pathways

“…Work on the accommodative response indicates that binocular combination there is approximately linear (Flitcroft et al, 1992), and can even cancel when signals are in antiphase (we did not try this configuration here). In the auditory system, interaural suppression of amplitude modulation also appears to be weak when measured using a similar steady-state paradigm (Baker et al, 2020). Finally, psychophysical matching experiments using static stimuli also show near-linear behaviour for luminance increments (Anstis and Ho, 1998; Baker et al, 2012; Levelt, 1965), though not for luminance decrements (Anstis and Ho, 1998).…”