![]() All three monkeys were extensively overtrained on the auditory and visual tasks for 1 to 2 years before the start of this study, and all had considerably more.Brain injury is a serious clinical problem. The monkeys were also trained on a procedurally identical visual DMS task. Pressing on nonmatching trials or withholding presses on matching trials, both defined as incorrect responses, were punished by extinguishing the lights within the chamber for 60 s. Correct responses on non-matching trials (HT-LT and LT-LT), which required withholding presses to the lever during the response window, were not rewarded. A correct response on matching trials (HT-HT and LT-LT) consisted of pressing the lever above the left speaker during the response window, which resulted in delivery of a 190-mg banana pellet. This was followed by presentation of the comparison stimulus from the speaker located on the left side of the front wall for a maximum period of 3 s (0.4-s listening period and a 2.6-s response window). After a 2-s listening period, the first press to the lever located above the right speaker terminated the sample stimulus and initiated a delay interval. At the end of a 20-s intertrial interval the sample stimulus (HT or LT) was presented by means of a speaker located on the right side of the front wall of the chamber. Three Cebus apella monkeys, ranging in age between 7 and 9 years, were trained on a successive auditory delayed matching-to-sample (DMS) task with a 3676-Hz high-frequency tone (HT) and a 243-Hz low-frequency tone (LT) as stimuli. ![]() We report now that when monkeys are trained in such a task, lesions of the superior temporal cortex severely impair their auditory short-term memory, yet have no effect on their visual memory. Although most attempts at training monkeys in this manner have met with failure, we succeeded by using monkeys that had extensive experience discriminating complex auditory stimuli. To ensure that auditory memory is being assessed, both the sample and comparison stimuli must be auditory. The absence of any clear auditory memory impairments after lesions to the superior temporal cortex may have resulted because the monkeys coded and retained the appropriate comparison stimulus rather than the sample stimulus during the delay period, thereby solving the task by engaging visual or spatial, rather than auditory, memory processes. In the few studies that have addressed this issue, monkeys were trained on tasks in which the sample stimuli were acoustic and the comparison stimuli were either visual or spatial. Although there is some evidence that damage to the superior temporal cortex, the highest order cortex of the auditory system, impairs auditory discriminative functions, there has been no convincing evidence that such lesions cause deficits in auditory short-term memory. Auditory Association Cortex Lesions Impair Auditory Short-Term Memory in MonkeysÄAMAGE TO THE INFERIOR TEMPOral cortex, the highest order visual cortex, impairs performance on both visual discrimination and visual short-term memory tasks, indicating that this region is important for both the perception and memory of visual information.
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