Auditory Objects In A Complex Acoustic Environment Rachele Malavasi, PhD Institute for Coastal Marine Environment (National Research Council) Oristano section, Italy Funded by CNR ISE Institute for Ecosistem Studies National Research Council the case of bird choruses In collaboration with: Department of Human Sciences, Environment and Nature (DiSUAN) University of Urbino

ASA: suite of auditory processes invoked to explain how humans and other animals organize the perception of complex acoustic environments into different sources/relevant events (Bregman 1990, Hulse et al. 1997) Auditory scene analysis in a glance In many animal species, similar to humans: starlings (MacDougall-Shackleton et al. 1998; Bee & Klump 2004, 2005) and other birds; frogs (Gerhardt & Huber 2002); goldfish (Fay 1998, 2000); macaques (Izumi 2001); bats (Schul & Sheridan, 2006) Auditory objects: perceptually coherent representations of sounds, that build-up over time / Streams: a perceptually-bound collection of sounds that together constitute an event (Bregman 1990) Streaming: separation of incoming auditory information into behaviorally relevant groups, or streams. Under most natural conditions this process equates to the separation of streams based on originating source (Knudsen 2010).

Perception of coordinated vocalizations Brumm & Slater 2007 Malavasi & Farina 2012 Synchronized conspecific choruses of tropical songbirds: - 3 individuals (Seddon 2002) - 4 or 5 individuals (Mann et al. 2006). Perception of objects or combinations of objects (Griffiths and Warren 2004) ECONOMIC 1 set of coordinated vocalizations (choral unit) = 1 perceptual group with different sources Cusack et al. 2004

Perceptual units in coordinated choruses Malavasi & Farina choral unit = 1 perceptual group Evolution selected individuals that are more skilled at learning heterospecific songs (Malavasi & Farina 2012)

Why coordinated choruses Interspecific coordinated choruses: provide public information (quality) and location cues (presence) influence of communicative processes on the composition of the community (Goodale et al. 2010; Malavasi et al. 2013) Participants preserve a shared neighbourhood of mutually supportive individuals (see Malavasi and Farina 2013), due to which they may hold longer their territory Dear Enemy Model (Fisher 1954, Temeles 1994) Getty 1987 Like with duets between mates, coordinated choruses seem to connect the structure of the signal to its function (in duets, Brumm & Slater 2007) Experience of each others songs, investment of time, energy (Malavasi & Farina 2012) Malavasi et al. 2013

Channelling theory of stream segregation Tonotopic organization of auditory stream: attivation of groups of close neurons determines the perception of tokens in one stream (a, c) (Beauvois & Meddis, 1991, 1996; Hartmann and Johnson, 1991; McCabe & Denham, 1997) If the evoked neural responses are temporally coherent, a single stream is perceived (b) (Elhihali et al. 2009) Coherence average measure (d-f) Bee & Mycheil 2008 Shamma et al The perceptual organization of a scene evolves over time

Temporal coherence Temporal-coherence analysis stage computes correlations among the outputs of the different feature-selective neurons (Shamma et al. 2011) Shamma et al Coherence is an average measure selection of a proper window for temporal-coherence analysis

Perceptual grouping vs selective attention Winkler et al. 2009, modified Introduction of TOP-DOWN PROCESSES (attention, memory, learning) depend on the listeners experience and expectations Selective attention: requires knowledge of the characteristics of the target of interest (Cusack et al. 2004) Selective attention is under conscious control of the listeners; dependent on the listeners experience in selecting the same auditory pattern (Cusack et al. 2004) Large windows…how much? Perception is about building testable hypothesis of the reality, based on prior knowledge and current sensory input (Gregory 1980)

Selective attention Selective attention emergence of relevant patterns Auditory inputs Objective information Top-down processes (memory, voluntary bias, learning) Individual history Context effect Ecological niche Subjective information (individually meaningful patterns) Streams are formed automatically or pre-attentively Selective attention mediates between current reality, cognitive processes and the auditory input Bottom-up processes (neural responses, feature analysis, temporal coherence analysis) SELECTIVE ATTENTION Attention + perceptual grouping ECONOMIC strategy for ASA PERCEPTUAL GROUPING

Perception of coordinated vocalizations Coordinated vocalizations: 1. analysis of feature stimulus-driven Winkler et al Perceptual grouping of coordinated vocalizations is mediated by attention Perceptual grouping of coordinated vocalizations is economic 2. selective attention stored knowledge and present reality 3. perceptual grouping within coherent temporal windows (regularities)

Songscope 2.4

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6/24/13