Traditionally, working memory and its neural underpinnings have been studied in the visual domain. A rich and diverse amount of research has investigated the lateral prefrontal cortex (lPFC) as a primary area for visual working memory, while another line of research has found the neurotransmitter acetylcholine (ACh) to be involved. This dissertation used auditory cues and found similar patterns of activity for processing auditory working memory information within a task compared to visual working memory processes. The first two experimental chapters demonstrated that the cholinergic system is involved in auditory working memory in a comparable fashion to its role in visual working memory. In chapter 2, blocking ACh impaired performance on an auditory working memory task in a dose dependent manner. Chapter 3 investigated the specificity of the effect of blocking ACh by administering an ACh agonist (physostigmine) at the same time as an ACh antagonist (scopolamine). When both drugs were administered together performance on the delayed matching-to-sample task (DMTS) task improved compared to performance on scopolamine alone. These results support the hypothesis that ACh is involved in auditory working memory. Chapter 4 investigated the neural correlates of auditory working memory in area 46 and found that this region of the lPFC contains neurons that are responsive to auditory working memory components in a very similar way to how it this region encodes information during visual working memory tasks. Neurons in the lPFC are responsive to visual or auditory cues, the delay portion of tasks, the wait time (i.e. decision making period), response, and reward times. This type of coding provides support for the theories that position the lPFC as a key player in recognition and working memory regardless of modality.

Five humans were exposed to a matching to sample task in which the delay (range = 0 to 32 seconds) between sample stimulus offset and comparison onset was manipulated across conditions. Auditory stimuli (1” tone) and arbitrary symbols served as sample stimuli for three (S1, S2, S3) and two (S4 and S5) subjects, respectively. Uppercase English letters (S, M, and N) served as comparison stimuli for all subjects. Results show small but systematic effects of the retention interval on accuracy and latency to selection of comparison stimuli. The results fail to show a difference between subjects exposed to auditory and visual sample stimuli. Some reasons for the failure to note a difference are discussed.

The present experiment was conducted to investigate the effects of reinforcer magnitude on resistance to disruption of remembering and response rates. Pigeons were exposed to a variable-interval (VI), delayed-matching-to-sample procedure (DMTS) with two components (rich and lean). Specifically, completion of a VI 20 second (s) multiple schedule resulted in DMTS trials in both components. In a DMTS trial, a choice of one of two comparison stimuli (e.g., blue key) results in reinforcement if the choice matches some property of the sample stimulus presented previously. Sample and comparison stimuli are separated by a delay. Four delays (0.1, 4, 8, and 16 s) were used between the sample and comparison stimuli in the study. The difference between rich and lean components was the length of hopper duration following a correct response. The probability of reinforcement following a correct response in both components was .5. Each pigeon was exposed to 50 sessions of initial baseline and then 30 sessions of baseline between each disruptive condition (extinction, intercomponent interval [ICI] food, lighting the houselight during delays, and prefeeding). Separable aspects of the forgetting functions (initial discriminability and rate of forgetting) were examined by determining accuracy at each delay. During baseline, response rates were higher in the rich component relative to the lean. Accuracy decreased as delay increased in both rich and lean components, and accuracy was consistently higher in the rich relative to the lean component. During disruptive conditions, extinction, ICI food, and prefeeding disrupted response rates, but lighting the houselight during the delays had little effect. During the DMTS portion of the procedure, extinction and prefeeding decreased initial discriminability and lighting the houselight during the delay increased rate of forgetting. Intercomponent food had little effect on accuracy. Accuracy in the rich component was more resistant to disruption relative to the lean component during extinction. These results indicate that certain disruptors do not have the same disruptive effect across response rates and accuracy (e.g., ICI food). These data also suggest that when systematic differences in accuracy between rich and lean components are revealed, performance in the rich component tends to be more resistant to disruption.

If remembering is discriminative behaviour along the dimension of time and if, as Sargisson and White (2001) argued, generalisation around a peak can occur in this behaviour, then the peak shift which has been shown in discrimination along so many other stimulus dimensions, might also occur in remembering. To examine this hypothesis, 6 hens were trained in a delayed matching-to-sample procedure at delays of 2 and 4 s. The probability of reinforcement for correct responses was initially 0.9 at both delays until performance stabilised. A generalisation probe was then carried out by inserting unreinforced trials at delays of 0, 1, 1.5, 2.5, 3, 3.5, 4.5, 5 and 6 s in a session amongst normal training delay trials. The generalisation functions had a slight peak around 2 s. After further training, a second generalisation probe showed a slightly declining function. The probability of reinforcement at the 2 s delay was then dropped to 0.1, so that in the terms of the classical generalisation/peak shift paradigm, 2-s delay trials became S¯ and 4-s delay trials became S+. A third generalisation probe then was conducted. This resulted in a flat function from 0 s to 3 s, and a large, clear peak in discriminative performance at 4.5 s over all hens. After more of the same differential reinforcement training, a fourth generalisation probe showed a broad curve peaking at 3 s, with minima at 1 s and 6 s and a global maximum at 0 s. Another training condition was then run, with the probability of reinforcement at the 2-s delay dropped to 0, to see if increasing the aversiveness of S¯ would again result in a peak shift. A fifth generalisation probe was then conducted. This showed a sharp decline in discriminability at shorter delays, a dip around 2 s, and a very small area shift beyond 4 s, but no clear peak shift. This was interpreted as being due to overlearning, with the consequences of remembering at S¯ no longer significantly affecting performance at S+. A final training condition was then run, with S¯ moved from 2 s to 3 s with zero probability of reinforcement, and for only a short period, to prevent overlearning. It was predicted that this would cause peak shift to re-occur. A sixth generalisation probe was then conducted. This found a further decline in discriminability at shorter delays, a shift in the dip from 2 s to 3 s, and a large, clear peak at 4.5 s. This demonstration of peak shift in a remembering process would not have been predicted by any traditional theory of memory, but strongly supports the conception of remembering as discriminative behaviour along the stimulus dimension of time.