Auditory Figure-Ground Segregation is Impaired by High Visual Load

Abstract

Figure-ground segregation is fundamental to listening in complex acoustic environments. An ongoing debate pertains to whether segregation requires attention or is ‘automatic’ and pre-attentive. In this magnetoencephalography (MEG) study we tested a prediction derived from Load Theory of attention1 that segregation requires attention, but can benefit from the automatic allocation of any ‘leftover’ capacity under low load. Complex auditory scenes were modelled with Stochastic Figure Ground stimuli (SFG2) which occasionally contained repeated frequency component ‘figures’. Naive human subjects passively listened to these signals while performing a visual attention task of either low or high load. Whilst clear figure-related neural responses were observed under conditions of low load, high visual load essentially abolished the neural response to the figure in auditory cortex (Planum Temporale, Heschl’s gyrus). We conclude that fundamental figure-ground segregation in hearing is not automatic but draws on shared resources across vision and audition.

Simultaneous auditory agnosia: Systematic description of a new type of auditory segregation deficit following a right hemisphere lesion

“…in several studies (Molloy, Lavie, & Chait, 2019;O'Sullivan, Shamma, & Lalor, 2015). We 568 suggest that the deficit here is in fundamental auditory segmentation that affects multiple 569 auditory cognitive domains based on the demonstrated lesion in auditory cortex.…”

Visual load does not decrease the auditory steady‐state response to 40‐Hz amplitude‐modulated tones

“…Accordingly, if it is assumed that 40‐Hz ASSRs comprise an overlap of wave V from the brainstem and MLR (in line with the superposition hypothesis), the ASSRs in the present research did not differ with load and task because we recorded responses that happen before the filtering occurred. However, because primary auditory cortex is the main generator of 40‐Hz ASSRs (Brugge et al, 2009; Engelien, 2000; Gutschalk, 1999; Herdman, 2002; Pantev, 1996; Ross, Miyazaki, & Fujioka, 2012), this explanation would be inconsistent with findings that load affects activations related to figure‐ground segregation in the auditory cortex, as measured with magnetoencephalography (Molloy, Lavie, & Chait, 2019).…”

Does auditory processing rely on encapsulated, or domain-general computational resources?

“…This was interpreted as indicating that high visual load reduced the gain on early auditory responses by depleting resources critical for auditory sensory processing. Molloy et al [11] (see also [12]) further showed that high load can severely impair computations associated with auditory figure-ground segregation, with effects observed from the earliest stages of processing in auditory cortex (see also [13]). Overall, these results point to the fact that what we may commonly consider as inherently auditory processes [14,15] actually draw on general computational capacity such that they can be affected by visual perceptual load.…”

“…Brain imaging can overcome this challenge by recording brain responses to ignored and entirely task irrelevant stimuli while participants are fully engaged in a primary task. Emerging evidence indeed demonstrates that visual load can affect auditory processing from relatively early cortical (but likely not subcortical; see [8]) processing stages [9][10][11].…”

“…There could be many reasons for this including the specific paradigms used. Indeed, Molloy et al [10,11] used paradigms in which the presentation of the visual and auditory stimuli were precisely aligned such that sounds were presented at the point within the visual trial where the demands on computational resources were highest. One might argue that most natural tasks do not involve such precisely timed auditory and visual stimulation and hence the actual effect of load on hearing in realistic situations may be modest (e.g.…”