The directional detection of an incident sound wave involves the processing of acoustic cues such as the interaural time and amplitude differences.
Some insects are very small, and yet, they are endowed with a keen sense of directional hearing.
In a parasitoid fly that detects and locate her host acoustically, the ears are set 0.520 mm apart. In effect, the tympanal membranes undergo vibrations similar to that of a flexible seesaw. Asymmetrical deflections could be shown to result from the mechanical coupling between the tympanal membranes. As an evolutionary innovation that also constitutes a novel functional principle for directional hearing, thus far known only in flies, the mechanism of intertympanal coupling relies on a morphological adaptation that permits, without the intervention of neural processing, the conversion of small acoustic cues into mechanical time and amplitude differences large enough to be subsequently processed by the nervous system. This mechanism illustrates, in the context of auditory research, the role of morphology in the functional adaptation of sensory systems.