Auditory Objects In A Complex Acoustic Environment

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

2. Auditory scene analysis in a glance • 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) • 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).

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

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

5. Why coordinated choruses Malavasi et al. 2013 Getty 1987 • 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) • 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 other’s songs, investment of time, energy (Malavasi & Farina 2012) • 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)

6. Channelling theory of stream segregation • If the evoked neural responses are temporally coherent, a single stream is perceived (b) (Elhihali et al. 2009) • 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) • Coherence average measure (d-f) • The perceptual organization of a scene evolves over time Bee & Mycheil 2008 Shamma et al. 2011

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

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

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

10. Perception of coordinated vocalizations Winkler et al. 2009 • Coordinated vocalizations: 1. analysis of feature stimulus-driven 2. selective attention stored knowledge and present reality 3. perceptual grouping within coherent temporal windows (regularities) • Perceptual grouping of coordinated vocalizations is mediated by attention • Perceptual grouping of coordinated vocalizations is economic

11. Songscope 2.4

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