Differential Influence of Frequency, Timing, and Intensity Cues in a Complex Acoustic Categorization Task

Abstract

Nagel KI, McLendon HM, Doupe AJ. Differential influence of frequency, timing, and intensity cues in a complex acoustic categorization task. J Neurophysiol 104: 1426 -1437, 2010. First published July 7, 2010 doi:10.1152/jn.00028.2010. Songbirds, which, like humans, learn complex vocalizations, provide an excellent model for the study of acoustic pattern recognition. Here we examined the role of three basic acoustic parameters in an ethologically relevant categorization task. Female zebra finches were first trained to classify songs as belonging to one of two males and then asked whether they could generalize this knowledge to songs systematically altered with respect to frequency, timing, or intensity. Birds' performance on song categorization fell off rapidly when songs were altered in frequency or intensity, but they generalized well to songs that were changed in duration by Ͼ25%. Birds were not deaf to timing changes, however; they detected these tempo alterations when asked to discriminate between the same song played back at two different speeds. In addition, when birds were retrained with songs at many intensities, they could correctly categorize songs over a wide range of volumes. Thus although they can detect all these cues, birds attend less to tempo than to frequency or intensity cues during song categorization. These results are unexpected for several reasons: zebra finches normally encounter a wide range of song volumes but most failed to generalize across volumes in this task; males produce only slight variations in tempo, but females generalized widely over changes in song duration; and all three acoustic parameters are critical for auditory neurons. Thus behavioral data place surprising constraints on the relationship between previous experience, behavioral task, neural responses, and perception. We discuss implications for models of auditory pattern recognition.

Auditory Forebrain Neurons Track Temporal Features of Time-Warped Natural Stimuli

“…In behavioral experiments, we found that birds were able to discriminate time-warped stimuli up to a factor of two significantly over chance level. These data are consistent with a recent behavioral study in female birds (Nagel et al 2010). This behavioral capacity motivated the search for an underlying neural basis for time-warp invariance.…”

“…We used the same pairs of songs for all subjects here, which leads to a possibility of pseudoreplication. However, in the previous study (Nagel et al 2010), a different set of songs was used and behavioral results were strikingly consistent with those here (for the subset of time warps tested).…”

“…Due to training restrictions, in both this study and a previous behavioral study (Nagel et al 2010), only two songs were used. It is possible subjects relied on a single feature in each of the songs, rather than the entire song, to make their choice.…”

“…Here, we examine the problem of time-warp invariance in songbirds (zebra finch), a model system which shows striking similarities to humans (Doupe and Kuhl 1999;Wang et al 2010) and which has previously shown behavioral invariance to time warping (Nagel et al 2010). We investigate neural responses in field L, a region homologous to mammalian primary auditory cortex, to variations introduced by time warping, where the stimulus is sped up or slowed down while preserving pitch.…”

Zebra finches are sensitive to prosodic features of human speech

“…There is, indeed, evidence that some songbirds are sensitive to variation in pitch, amplitude and song syllable duration in their natural song [11]. Also, some mammal and bird species show a sensitivity to the general prosodic patterns in human speech [12][13][14][15][16].…”