The representation of auditory space in the cerebral cortex: Possible implications for the formation of auditory objects

Information about the identity and location of sound sources is conveyed by spectral and temporal features of the sound wave and by interaural dispari ty and other acoustic cues, respectively. One aspect of the process referre d to as the "formation of auditory objects" is the fusion of different feat ures of the acoustic signal into the central representation of an object at a particular location. A second aspect is the ability to segregate a compl ex acoustic scene into the various objects comprising the scene. The major clue to the azimuthal location of high-frequency sound sources is provided by interaural intensity differences (IIDs), and neurons in the mammalian pr imary auditory cortex (Al) exhibit corresponding forms of sensitivity to II Ds and to the azimuthal location of free-field sound sources. The two major forms of such sensitivity seen in Al are also exhibited by midbrain neuron s in the deep layers of the superior colliculus. However, while neurons exh ibiting these different forms of sensitivity are distributed along frequenc y-band strips in Al in a patchy fashion, in the superior colliculus they ar e organized in a highly systematic fashion to produce a place map of audito ry space. A similar contrast between an orderly midbrain map and a patchy f orebrain representation of auditory space is seen in the barn owl It is sug gested that these different forms of organization relate to the different f unctions of auditory spatial representation in the two structures, and that patchy cortical organization in mammals might contribute to the integratio n of information across frequency band strips and cortical fields that is n ecessary for the formation of auditory objects.