A PERIOD OF SENSORY STIMULATION may alter the perception of subsequent sensory events. After sounds, for example, there may be changes in threshold (19), in the quality of acoustic sensation (20, 29), or tinnitus (20). The neurophysiological mechanisms underlying these alterations in sensation are not well understood. Working with cats, Starr and Livingston (30) described a profound and reversible suppression of summated spontaneous activity in subcortical stations of the auditory pathway as an aftereffect of sustained sound exposure. The period of altered spontaneous activity lengthened as the intensity or duration of the sound was increased. The experiments on single units in cochlear nucleus presented in this report were undertaken to define more precisely the relationship between the physical parameters of the sound stimulus and the period of altered spontaneous activity.

IT IS NOW possible to record in humans the electrical activity generated along the auditory pathway in its course from the cochlea to the cortex using surface electrodes (Jewett). The principle employed is that of "far-field" recording and entails using a small computer to average the potentials generated-at a distance out of the background electrical noise. Approximately 1,000 to 2,000 click trials presented at 10 per second are necessary to resolve the brain-stem components.

The Western medical profession's knowledge concerning the development of Soviet medicine during the preceding two decades 1s ~ost meager. This situation may be attributed to scvct;al factors. First, there was a paucity of pertinent material available for study during this period due to the r~tri~tions imposed upon the exchange of sc1ent1fic data between Russia and \'cstcm Nations. In addition, as a result o( the exigencies of war and politics, the . inter· change of competent and interested obse.Vers was reduced to an insignificant number. Furthermore, the lack of Western scientific personnel familiar with the Russian language limited the significance of the few Russian scientific journals which were available. And finally, the deficiencies of Russian medicine evident during the initial years of Soviet rule may have minimized the value of any further exchange.

Some of the neurophysiological data for understanding the neural basis of sound localization are reviewed. There are single units at many levels of the auditory pathway that are sensitive to acoustic cues of interaural differences in time of arrival (Δt) and of intensity (ΔI). The unit sensitivities take the form of a gradual change in response probability over a limited portion of the Δt or ΔI continuum. The possibility that the response change supports a receptive field organization of auditory space similar to the neural analysis of the visual and somatosensory dimensions is rejected because of the gross character of the sensitivity. Most auditory units are 'tuned' to between 50 and 180° of auditory space, measures that are more than 10 fold greater than the usual psychoacoustic threshold. It is suggested that information about auditory space is contained in the difference of activity between populations of units sensitive to right sided and to left sided inputs which are segregated into the paired auditory nuclei. The comparators of the relative levels of activity of these paired nuclei are through segmental connections to various kinds of motor mechanisms tending to direct the animal to move in a lateralized manner.

What factors influence our ability to maintain the temporal order of sequences in visual working memory? We used task-evoked pupillometry to investigate how the semantic content and spatial positions of images influence memory for temporal order. We found that memory for temporal order was stronger for sequences consisting of semantically meaningful images compared to abstract images, but there was no memory benefit for presenting sequences from left-to-right compared to centrally or from right-to-left. In addition, we found that pupil dilation was greater for sequences of semantic images compared to abstract images and particularly for items later in the sequence and in sequences presented from left-to-right. These results highlight the utility of using pupillometry to study working memory processes and provide new insights into how the nature of the items to be remembered and the spatial positions of those items influence visual working memory for temporal order.