Auditory memory: a comparison between humans and starlings.

In this study, we compare the processing of acoustic signals in European starlings (Sturnus vulgaris) and in human listeners by observing the decay of short-term auditory memory in delayed non-matching-to-sample experiments. A series of identical "sample" stimuli and a final "test" stimulus were separated by variable delays (1 to 180.1 s). Subjects had to classify sample and test stimuli as being either the same or different. Test stimuli were pure tones that differed in a single signal feature, i.e., frequency, and song motifs that differed in multiple signal characteristics. We have tested several predictions concerning the memory performance of starlings and humans and we obtained the following outcome: (1) In contrast to our expectation, signal complexity had no effect. The overall analysis of the starling data did not show differences in memory performance for signals differing in single or multiple signal features. (2) Starling and human data supported the hypothesis that auditory memory impairs with increasing delay. This was also seen when interfering noise was added to the delay periods in an additional series with human subjects. (3) The starling data showed that the repetition of sample stimuli improved memory performance, compared to only a single presentation. Human memory performance, however, was similar for a single and for the repeated presentation of signals. (4) Differences in salience between sample and test stimuli were positively related to memory performance only for tonal stimuli but not for song motifs. Results are discussed with respect to a model based on signal detection theory and to requirements for the analysis of natural communication signals.