A recent study investigating the neural mechanisms underlying this dynamic spatial sensitivity in cats identified the primary auditory cortex (A1) as a potential locus for such dynamic sound location processing. For example, an auditory target is processed faster when auditory spatial attention is focused at the location of the target ( Spence and Driver, 1994 Mondor and Zatorre, 1995 Rorden and Driver, 2001). For this reason, cortical processing of sound location is presumably taking place in a functionally specialized, posterior-dorsal “where” stream ( Rauschecker and Tian, 2000 Tian et al., 2001 Arnott et al., 2004 Rauschecker and Scott, 2009).īehavioral evidence from psychophysical studies shows that auditory spatial sensitivity in humans is dynamic. These spatially-sensitive areas include the caudo-medial (CM) and caudo-lateral belt areas (CL) in nonhuman primates ( Tian et al., 2001), the posterior auditory field ( Harrington et al., 2008) and dorsal zone in cats ( Stecker and Middlebrooks, 2003 Stecker et al., 2005 Lomber and Malhotra, 2008), and the planum temporale (PT) in humans ( Warren and Griffiths, 2003 Brunetti et al., 2005 Deouell et al., 2007 van der Zwaag et al., 2011 Derey et al., 2016 McLaughlin et al., 2016). In the mammalian auditory cortex, neural activity in posterior areas is modulated by sound location more than in primary and anterior areas. Sound localization is a crucial component of mammalian hearing. These findings suggest that the hierarchical view of cortical functional specialization needs to be extended: our data indicate that active behavior involves feedback projections from higher-order regions to primary auditory cortex. Our results provide compelling evidence that active behavior (sound localization) sharpens spatial selectivity in primary auditory cortex, whereas spatial tuning in functionally specialized areas (PT) is narrow but task-invariant.
However, this model is based mostly on passive listening studies. Posterior-dorsal cortical auditory areas, planum temporale (PT) in humans, are considered to be functionally specialized for spatial processing.
Passive audio tuner series#
SIGNIFICANCE STATEMENT According to a purely hierarchical view, cortical auditory processing consists of a series of analysis stages from sensory (acoustic) processing in primary auditory cortex to specialized processing in higher-order areas. As such, our findings suggest that the hierarchical model of auditory processing may need to be revised to include an interaction between primary and functionally specialized areas depending on behavioral requirements. These results indicate that changes of population activity in human primary auditory areas reflect dynamic and task-dependent processing of sound location. In PT, decoding accuracy was not modulated by task performance. We further applied a population pattern decoder to the measured fMRI activity patterns, which confirmed the task-dependent effects in the left core: sound location estimates from fMRI patterns measured during active sound localization were most accurate. In contrast, spatial tuning in PT was sharp but did not vary with task performance. Yet, our results show that spatial tuning profiles in primary auditory cortical areas (left primary core and right caudo-medial belt) sharpened during a sound localization (“where”) task compared with a sound identification (“what”) task. According to the hierarchical model of auditory processing and cortical functional specialization, PT is implicated in sound location (“where”) processing. Using functional magnetic resonance imaging (fMRI), we assessed how active behavior affects encoding of sound location (azimuth) in primary auditory cortical areas and planum temporale (PT). Spatial hearing sensitivity in humans is dynamic and task-dependent, but the mechanisms in human auditory cortex that enable dynamic sound location encoding remain unclear.
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