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Partially segregated neuronal pathways ("what" and "where" pathways, respectively) are thought to mediate sound recognition and localization. Less studied are interactions between these pathways. In two experiments, we investigated whether near-threshold pitch discrimination sensitivity (d') is altered by supra-threshold task-irrelevant position differences and likewise whether near-threshold position discrimination sensitivity is altered by supra-threshold task-irrelevant pitch differences. Each experiment followed a 2 x 2 within-subjects design regarding changes/no change in the task-relevant and task-irrelevant stimulus dimensions. In Experiment 1, subjects discriminated between 750 Hz and 752 Hz pure tones, and d' for this near-threshold pitch change significantly increased by a factor of 1.09 when accompanied by a task-irrelevant position change of 65 micros interaural time difference (ITD). No response bias was induced by the task-irrelevant position change. In Experiment 2, subjects discriminated between 385 micros and 431 micros ITDs, and d' for this near-threshold position change significantly increased by a factor of 0.73 when accompanied by task-irrelevant pitch changes (6 Hz). In contrast to Experiment 1, task-irrelevant pitch changes induced a response criterion bias toward responding that the two stimuli differed. The collective results are indicative of facilitative interactions between "what" and "where" pathways. By demonstrating how these pathways may cooperate under impoverished listening conditions, our results bear implications for possible neuro-rehabilitation strategies. We discuss our results in terms of the dual-pathway model of auditory processing.

Abstract The human supratemporal plane contains the primary as well as several other auditory areas. We have investigated the intrinsic connectivity of these areas by means of antero- and retrograde labelling with the carbocyanin dye DiI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate). A total of 30 injections was placed in both hemispheres of four freshly fixed postmortem brains. Labelled neurons and axons were found in cortex around the injection. The retrograde labelling varied from faint to Golgi-like; most of the retrograde labelled neurons were layers II–III pyramids and only a few were nonpyramidal neurons. Labelled axons were dense in all layers near the injection site, while they became relatively rare in layer IV further away. The tangential spread of labelling differed among auditory areas. On Heschl's gyrus (corresponding to the primary auditory cortex and cytoarchitectonic areas TD and part of TB) intrinsic connectivity involved a relatively narrow part of cortex. They spread over larger parts of cortex in plana polare and temporale (areas TG, TA and the remaining part of TB). A number of injections also produced anisotropic labelling patterns. These results reveal differences in intrinsic connectivity between auditory areas. They suggest that intrinsic connections within the primary auditory area, area TD and part of TB that is on Heschl's gyrus, involve mainly nearby units or modules, probably with similar coding properties, whereas in surrounding areas, connections spread over more distant units and may play an important role in the integration of different auditory features. [ABSTRACT FROM AUTHOR]

Abstract The human primary auditory cortex (AI) is surrounded by several other auditory areas, which can be identified by cyto-, myelo- and chemoarchitectonic criteria. We report here on the pattern of calcium-binding protein immunoreactivity within these areas. The supratemporal regions of four normal human brains (eight hemispheres) were processed histologically, and serial sections were stained for parvalbumin, calretinin or calbindin. Each calcium-binding protein yielded a specific pattern of labelling, which differed between auditory areas. In AI, defined as area TC [see C. von Economo and L. Horn (1930) Z. Ges. Neurol. Psychiatr., 130 , 678–757], parvalbumin labelling was dark in layer IV; several parvalbumin-positive multipolar neurons were distributed in layers III and IV. Calbindin yielded dark labelling in layers I–III and V; it revealed numerous multipolar and pyramidal neurons in layers II and III. Calretinin labelling was lighter than that of parvalbumin or calbindin in AI; calretinin-positive bipolar and bitufted neurons were present in supragranular layers. In non-primary auditory areas, the intensity of labelling tended to become progressively lighter while moving away from AI, with qualitative differences between the cytoarchitectonically defined areas. In analogy to non-human primates, our results suggest differences in intrinsic organization between auditory areas that are compatible with parallel and hierarchical processing of auditory information. [ABSTRACT FROM AUTHOR]