Communication

Communication is a distinctly temporal behavior. It requires transmitting signals in sequence and duration such that a receiving organism understands the message.

There are cases when the timing of symbolic components is unimportant, for example, when one is merely trying to get another's attention. Here we are interested in the relationship between syntactical elements in time and the way in which that conveys information. More specifically, we are interested in animals that learn how to communicate.

Songbirds acquire songs by listening to other birds (Beecher et al., 1998). The primary reason for this appears to be ecological. For song sparrows, the song repertoire is usually learned after the bird leaves its birthplace and during the first season of territory establishment (Beecher, 1994). In this way, the song sparrow learns the social communication strategies of its neighbors. This is further evidenced by song sparrows showing a preference for the learning of already shared songs (Beecher et al., 1998).

The fact that birds can learn frequency and durational components of a song implies a usefulness for event timing (see MacDonald and Meck, this volume). If one bird intends to mimic the call of another, then it must be able to record that call in memory. Functionally, the mechanism that records the call is an event timer; it learns the sequence and duration of notes that constitute the local song. Whether this ability can be generalized to record the times of nonsyntactic events remains to be established.

Linguistic studies in humans recognize a temporal component, but a clear understanding of exactly how that component is manifested is far from understood (Port et al., 1995). Some models of language acquisition are distinctly similar to contemporary models of hippocampal function in their use of recurrent networks (Port et al., 1995; Wallenstein et al., 1998). There is also evidence that perceived time is shorter for familiar auditory signals than it is for unfamiliar signals, suggesting that perceived time is not absolute for auditory signals but is influenced by the content of the perceived signal (Kowal, 1984). The main difficulty with results from linguistic studies, as it is for essentially all studies on communication, is that it is extremely difficult to separate the meaning from the message.

Insect communication is understood to carry information in its gross rhythms. There is evidence that insects distinguish likely mates by the gaps between signals, the interpulse interval (Kyriacou et al., 1992; Michelsen et al., 1985). In the case of Drosophila the interpulse interval appears to be under genetic control with a well-defined relationship with circadian rhythms (see Section 4.3.3).

What about the receiver? Moths are useful for studying auditory transduction because they have a relatively simple ear, with one or two receptor cells attached to an accessible tympanum. In moths, specific cells can operate as frequency filters (Michelsen et al., 1985), tuned to specific sensory stimuli. Pattern-sensitive neurons have also been observed in the pyloric network of lobster (Hooper, 1998). The presence of such neurons in D. melanogaster would explain stable female preferences despite differences in the circadian schedule. In this way, invertebrates may bypass the need for the higher cortical functioning that goes along with vertebrate event timers.

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