Does common spatial origin promote the auditory grouping of temporally separated signal elements in grey treefrogs?

Abstract

‘Sequential integration’ represents a form of auditory grouping in which temporally separated sounds produced by the same source are perceptually bound together over time into a coherent ‘auditory stream’. In humans, sequential integration plays important roles in music and speech perception. In this study of the grey treefrog (Hyla chrysoscelis), we took advantage of female selectivity for advertisement calls with conspecific pulse rates to investigate common spatial location as a cue for sequential integration. We presented females with two temporally interleaved pulse sequences with pulse rates of 25 pulses/s, which is half the conspecific pulse rate and more similar to that of H. versicolor, a syntopically breeding heterospecific. We tested the hypothesis that common spatial origin between the two pulse sequences would promote their integration into a coherent auditory stream with an attractive conspecific pulse rate. As the spatial separation between the speakers broadcasting the interleaved pulse sequences decreased from 180° to 0°, more females responded and females exhibited shorter response latencies and travelled shorter distances en route to a speaker. However, even in the 180° condition, most females (74%) still responded. Detailed video analyses revealed no evidence to suggest that patterns of female phonotaxis resulted from impaired abilities to localize sound sources in the spatially separated conditions. Together, our results suggest that females were fairly permissive of spatial incoherence between the interleaved pulses sequences and that common spatial origin may be only a relatively weak cue for sequential integration in grey treefrogs.

Sound transmission and the recognition of temporally degraded sexual advertisement signals in Cope's gray treefrog (Hyla chrysoscelis)

“…Across all five tests, the mean response latencies ranged between 65s and 91s, and the fastest response latencies ranged between 30s and 38s; these latencies are fairly typical for this species (e.g. Bee and Riemersma, 2008). Together, these results suggest the following.…”

Spatial hearing in Cope’s gray treefrog: II. Frequency-dependent directionality in the amplitude and phase of tympanum vibrations

“…Several studies have now demonstrated spatial release from masking in Cope’s gray treefrogs, and have shown that it reduces response latencies and increases response probabilities in phonotaxis tests (Bee 2007b; Ward et al 2013a), reduces signal recognition thresholds (Nityananda and Bee 2012), and improves temporal pattern discrimination in the context of species recognition (Bee 2008; Ward et al 2013a). Studies of auditory grouping and auditory stream segregation in this species indicate spatial cues might be relatively more important for perceptually binding simultaneous signal components, such as the harmonics in the bimodal frequency spectrum of calls, than for binding sequentially produced signal components, such as pulses (Bee and Riemersma 2008; Bee 2010). While the present study represents an important first step, there is a clear need for additional investigations of the biomechanics and neurophysiology of spatial hearing in Cope’s gray treefrogs.…”

“…Spatial hearing is also important in other perceptual and cognitive tasks not directly related to sound source localization. Three such likely tasks involve auditory grouping (Schwartz and Gerhardt 1995; Farris et al 2002, 2005; Bee and Riemersma 2008; Bee 2010; Farris and Ryan 2011), spatial release from masking (Schwartz and Gerhardt 1989; Bee 2007b, 2008; Nityananda and Bee 2012; Ward et al 2013a), and cross-modal sensory integration (Narins et al 2005; Taylor et al 2011). …”

“…Recent behavioral studies of this species have focused on the performance of several different perceptual tasks dependent on spatial hearing, such as sound source localization (Caldwell and Bee 2014), spatial release from masking in signal recognition and discrimination tasks (Bee 2007b, 2008; Nityananda and Bee 2012; Ward et al 2013a), and auditory grouping and stream segregation based on spatial coherence (Bee and Riemersma 2008; Bee 2010). Ear directionality has been previously examined for only a single H. chrysoscelis individual (Jørgensen 1991; Jørgensen and Gerhardt 1991), precluding any description of the range of typical responses or of inter-individual variation.…”

Treefrogs as animal models for research on auditory scene analysis and the cocktail party problem

“…Frogs appear to group temporally separated components of their signals over wide angles of spatial separation (e.g., Farris et al, 2002, 2005; Farris and Ryan, 2011; Gerhardt et al, 2000a). Thus far, two studies have tested the hypothesis that spatial proximity promotes sequential integration in gray treefrogs ( H. chrysoscelis and H. versicolor ) (Bee and Riemersma, 2008; Schwartz and Gerhardt, 1995). Both studies used interleaved sequences of pulses to take advantage of the natural selectivity that females have for conspecific pulse rates, which are about twice as fast in H. chrysoscelis (35–50 pulses/s) compared with H. versicolor (19–24 pulses/s) (Gerhardt, 2001).…”