Effect of posttrial episodes on conditioning in compound conditioned stimuli

The effect of signaled and nonsignaled posttrial episodes (PTEs) on conditioning to the target CS of a preceding compound CS-US trial was examined in two conditioned emotional response (CER) experiments with rats. Experiment 1 revealed that a nonsignaled PTE, a second shock US, interfered with conditioning to the preceding target CS and that the interference effect of the PTE was greater when it occurred 5 sec as opposed to 1,800 sec after the preceding compound CS-US trial. Experiment 2 revealed that if the shock PTE was signaled by a CS, its ability to interfere with conditioning was reduced. This second study also revealed that omission of an "expected" US interfered with conditioning to the target CS. The implications of these data for information processing models of Pavlovian conditioning are discussed.     

Effects of acetoxycycloheximide on appetitive learning and memory

The effects of direct brain infusions of acetoxycycloheximide (an inhibitor of protein synthesis; ACXH) on acquisition, storage and recall of memory for one-trial appetitive learning were examined in five experiments. ACXH was infused into the rats' hippocampi through implanted cannulas. Control subjects received an equal volume of physiological saline. ACXH was infused (a) 5 h before acquisition, (b) 5 hr before commencement of recall tests, and (c) immediately after acquisition. Each subject's general motor activity was recording during testing. The results indicate that (1) ACXH has similar effects on appetitive and avoidance learning. (2) ACXH administered immediately after acquisition, has no effect on memory. (3) At 4 hr after acquisition memory is affected by ACXH. (4) Short-term memory is unaffected by ACXH and can exist independently of long-term memory. (5) ACXH consistently reduces general motor activity.     

Effects of modality preferences on learning and recall of bisensory stimuli

The performance of visual attenders and aural attenders, as defined by performance on a bisensory digit-span task, was compared on three bisensory tasks. First, in replication of an earlier study, performance was compared on a bisensory missing-unit paradigm, in which S was required to respond with missing units from two independent sets of stimuli, each set being presented on a separate channel. The results corroborated those of an earlier study in which an interaction between modality preferences and presentation modality was found. Further, differential recall patterns were found for each of the groups. While such comparable results were not found on the other two tasks, differential performance on a bisensory paired-associate task and a bisensory connected discourse task were found. The results are interpreted in accord with Murdock’s (1967) hypotheses concerning separate sensory storage mechanisms.     

Effects of category diversity on learning,memory, and generalization

In this study, we examined the effect of within-category diversity on people's ability to learn perceptual categories, their inclination to generalize categories to novel items, and their ability to distinguish new items from old. After learning to distinguish a control category from an experimental category that was either clustered or diverse, participants performed a test of category generalization or old-new recognition. Diversity made learning more difficult, increased generalization to novel items outside the range of training items, and made it difficult to distinguish such novel items from familiar ones. Regression analyses using the generalized context model suggested that the results could be explained in terms of similarities between old and new items combined with a rescaling of the similarity space that varied according to the diversity of the training items. Participants who learned the diverse category were less sensitive to psychological distance than were the participants who learned a more clustered category.     

Immediate memory and simultaneous stimuli

When two sets of digits are presented simultaneously one to one ear and one to the other, the subject may be asked to write them down from immediate memory beginning with those on an ear chosen by the experimenter. He can do this, but any mistakes are usually amongst those on the ear prescribed for later response. If the subject does not know the order of recall until after stimulation, he either shows low efficiency with the same serial order effect, or else normal efficiency with an altered serial order effect.

When the order of recall is known in advance, efficiency is also reduced by altering the time of presentation of the last items to be recalled; and also by inserting irrelevant items. All these facts are consistent with a particular theory of immediate memory.     

Effects of exposure on discrimination of similar stimuli and on memory for their unique and common features

Human participants received exposure to similar visual stimuli (AW and BW) that shared a common feature (W). Experiment 1 demonstrated that subsequent discrimination between AW and BW was more accurate when the two stimuli were preexposed on an intermixed schedule (AW, BW, AW, BW…) than when they were preexposed on a blocked schedule (AW, AW…BW, BW…): the intermixed-blocked effect. Furthermore, memory for the unique features of the stimuli (A and B) was better when the stimuli were preexposed on an intermixed schedule than when they were preexposed on a blocked schedule. Conversely, memory for the common features of the stimuli (W) was better when the stimuli were preexposed on a blocked schedule than when they were preexposed on an intermixed schedule. Experiment 2 again demonstrated the intermixed-blocked effect, but participants were preexposed to the stimuli in such a way that the temporal spacing between exposures to the unique features was equated between schedules. Memory for the unique and common features was similar to that found in Experiment 1. These findings support the proposal that perceptual learning depends on a mechanism that enhances memory for the unique features and reduces memory for common features.     

Effects of postresponse visual stimuli on visual discrimination learning in the rhesus monkey

To learn more about the mechanism (or mechanisms) involved with postresponse stimulus processing during discrimination learning, a series of studies was conducted with monkeys to determine why the combined relevant and irrelevant stimuli impair learning more than irrelevant stimuli appearing alone. It was found that: (a) the greater size and complexity of the combination of stimuli were not responsible for the greater deficit, while the presence of the relevant stimuli (S^D and S^Δ) within the stimulus combination apparently was; (b) the more similar the postresponse irrelevant stimuli were to the relevant stimuli the greater the deficit that resulted; and (c) monkeys that had earlier learned to discriminate the relevant and irrelevant features of a combination showed no learning impairment when this same stimulus combination was later presented after the response during a new learning problem. These results were interpreted as evidence that: (1) processes associated with learning a discrimination problem do not end with the execution of a choice response; (2) postresponse stimuli produce greater impairment in discrimination learning when they are distorted versions of the relevant stimuli; and (3) the impairment resulting from postresponse irrelevant stimuli occurs primarily when this misinformation is processed and misperceived as being relevant to learning the discrimination problem.     

Ecologically relevant stimuli and color memory

Ecologically relevant stimuli were developed as an alternative to Munsell color chips. Colored pictures of familiar objects were used to study color memory. We investigated the typicality of color to particular objects. Contextually typical colors were remembered more accurately than atypical colors were. Moreover, this variable had a stronger effect on memory than focality did. We concluded that memory for ecologically relevant material is more impressed by a color's relation to experience than by its intrinsic properties.     

Emotional stimuli exert parallel effects on attention and memory

Because emotional and neutral stimuli typically differ on non-emotional dimensions, it has been difficult to determine conclusively which factors underlie the ability of emotional stimuli to enhance immediate long-term memory. Here we induced arousal by varying participants' goals, a method that removes many potential confounds between emotional and non-emotional items. Hungry and sated participants encoded food and clothing images under divided attention conditions. Sated participants attended to and recalled food and clothing images equivalently. Hungry participants performed worse on the concurrent tone-discrimination task when they viewed food relative to clothing images, suggesting enhanced attention to food images, and they recalled more food than clothing images. A follow-up regression analysis of the factors predicting memory for individual pictures revealed that food images had parallel effects on attention and memory in hungry participants, so that enhanced attention to food images did not predict their enhanced memory. We suggest that immediate long-term memory for food is enhanced in the hungry state because hunger leads to more distinctive processing of food images rendering them more accessible during retrieval.