Structure and function of the codfish ear

The general anatomy of the codfish ear was examined in order togain an insight into the mode of hair cell stimulation. The ability to discriminate between frequencies in the apparent absence of a mechanical frequency analyser; and the directional hearing capabilities of codfish in the apparent absence of adequate interaural time, phase and intensity cues were the two main problems investigated.Using extracellular recording techniques, single units were recorded in the primary afferent fibres from various rami of the auditory nerve. The units were classed according to the types of spontaneous activity displayed. The frequency response of each type of unit was investigated by examining the change in spikes/second, spikes/stimulus cycle, and the degree of synchrony with the stimulus waveform, over a range of frequencies, at different stimulus amplitude levels. The directional characteristics of the units were investigated by rotating the fish relative to a fixed sound source, while recording the change in the auditory response. Central nervous processing of binaural sound stimuli was investigated by interrupting the auditory response, applying an electrical block to one or other of the two posterior saccular rami.The results are discussed in the light of the current state of knowledge of hearing in fish.