Do great tits assess rivals by combining direct experience with information gathered by eavesdropping?

Animals frequently use signals that travel further than the spacing between individuals. For every intended recipient of a given signal there are likely to be many other individuals that receive information. Eavesdropping on signalling interactions between other individuals provides a relatively cost-free method of assessing future opponents or mates. Male great tits (Parus major) extract relative information from such interactions between individuals unknown to them. Here, we show that male great tits can take information gathering a stage further and obtain more information about a previously unencountered intruder, by the hitherto unknown capability of combining information gathered by eavesdropping with that derived from their own direct interaction with an individual. Prior experience with an intruder (A) was achieved by subjecting a focal male to different levels of intrusion simulated using interactive playback. This intruder (A) then took part in a simulated interaction with an unknown male (B) outside the territorial boundary of the focal males. In response to subsequent intrusion by the second male (B), focal males showed low song output in response to males that had lost to a male that the subject was able to beat. Males of known high quality, or those about which information was ambiguous, elicited a high level of song output by focal males. We discuss the implications of this finding for the evolution of communication and social behaviour.

Male great tits eavesdrop on simulated male-to-male vocal interactions.

Animal communication generally occurs in the environment of a network of several potential signallers and receivers. Within a network environment, it is possible to gain relative information about conspecifics by eavesdropping on signalling interactions. We presented male great tits with the opportunity to gain such information by simulating singing interactions using two loudspeakers. Interactions were presented so that relevant information was not available in the absolute singing behaviour of either individual, only in the relative timing of their songs in the interaction as a whole. We then assayed the information extracted by focal males by subsequently introducing one of the 'interactants' (i.e. loudspeakers) into the territory of the focal male. Focal males responded with a reduced song output to males that had just 'lost' an interaction. Focal males did not respond significantly differently to 'winners' as compared with intruders recently involved in an interaction that contained no consistent information. Focal males also responded by switching song types more often when encountering males that had recently been involved in a low-intensity interaction. These results provide the clearest evidence yet that male songbirds extract information from signal interactions between conspecifics in the field.

Three experimental measures of a digital beamforming signal processing algorithm.

Three studies were conducted to evaluate a prototype nonlinear digital beamforming hearing aid. The experiments all used contextually rich speech materials and subjective analysis methods and, on that basis, are grouped together in this report. In experiment 1, the beamforming was done off line and subjects wore their own hearing aids in an attempt to determine whether the processing reduced the interference of noise jammers. In experiments 2 and 3, subjects used portable, head-worn, real-time devices. The results of these experiments showed improvements in perceived ease of speech understanding for these types of subjective measures and lend encouragement to further development of this type of binaural hearing aid. Additional work is also required to develop methods of physically characterizing the nonlinear directional properties of the algorithms.

Preference for potential tinnitus maskers: results from annoyance ratings.

Using the method of magnitude estimation, annoyance ratings of thirty-six different masking sounds obtained from a group suffering from tinnitus were compared with ratings from a normal-hearing group in an attempt to assess the acceptability of potential tinnitus maskers. The key findings were as follows: In both groups bandpass noise was rated as less annoying than tones or triangular waves. The annoyance value of bandpass maskers increased with bandwidth. Interrupted maskers were rated as more annoying than continuous maskers. Most of the differences between the tinnitus and normal group could be explained in terms of the high-frequency hearing loss and loudness recruitment associated with the tinnitus group. Control over the centre frequency and the bandwidth of a noise masker was important in optimising the acceptability of the tinnitus masker.

Parametric studies of tinnitus masking and residual inhibition.

A study was made of the relation between tinnitus masker composition (frequency, bandwidth, intensity duration) and the time course and magnitude of residual inhibition (RI). RI was determined by methods of (a) loudness estimation - where the subject varied the pointer position on a loudness scale (b) loudness balance - where the tinnitus loudness was maintained in loudness balance in the period following masking with a tone of variable intensity presented to the opposite ear. In addition, sensitivity change (temporary threshold shift, TTS) in the tinnitus and masker frequency regions was measured by determining tone thresholds (using a tracking technique) before and after masker presentation. The key findings were as follows: (I) RI depends on masker centre frequency. The frequency producing maximal RI is usually lower than the tinnitus frequency (as determined by pitch matching). (2) In some subjects only narrow-band noise produces RI. (3) RI is proportional to the masker intensity provided the tinnitus is completely masked; little or no RI is produced by a partial masker. (4) For the masker durations used (in the range 10 s to 10 min) RI duration is linearly related to the logarithm of masker duration. (5) A second masker presentation during RI does not potentiate RI. (6) Contralateral masking did not produce RI. (7) maskers producing RI also produce TTS around the tinnitus frequency. (8) The TTS magnitude and the time course of TTS appear to be related to RI.