Association between dyads and correct responses on the Paced Auditory Serial Addition Task (PASAT)

The sensitivity of the Paced Auditory Serial Addition Task (PASAT) to working memory deficits may be enhanced by examining "dyads" (i.e., correct responses immediately preceded by a correct response) as a complement to the traditional total correct summary score. In a sample of 397 mostly African American (79%) healthy adults, total dyad and total correct scores were highly correlated (r = .96, p < .001); however, the magnitude of this association diminished in faster stimulus presentation trials, particularly among participants with impaired working memory abilities.     

Release of inattentional blindness by high working memory load: elucidating the relationship between working memory and selective attention

An unexpected stimulus often remains unnoticed if attention is focused elsewhere. This inattentional blindness has been shown to be increased under conditions of high memory load. Here we show that increasing working memory load can also have the opposite effect of reducing inattentional blindness (i.e., improving stimulus detection) if stimulus detection is competing for attention with a concurrent visual task. Participants were required to judge which of two lines was the longer while holding in working memory either one digit (low load) or six digits (high load). An unexpected visual stimulus was presented once alongside the line judgment task. Detection of the unexpected stimulus was significantly improved under conditions of higher working memory load. This improvement in performance prompts the striking conclusion that an effect of cognitive load is to increase attentional spread, thereby enhancing our ability to detect perceptual stimuli to which we would normally be inattentionally blind under less taxing cognitive conditions. We discuss the implications of these findings for our understanding of the relationship between working memory and selective attention.     

Memory codes in pigeon short-term memory: Effects of varying the number of sample and comparison stimuli

In a delayed conditional discrimination task, pigeons can remember either some aspect of the conditional stimulus (i.e., they can code retrospectively) or some aspect of the stimulus to which they will respond at the end of the delay (i.e., they can code prospectively). To determine the nature of the memory code, we varied the number of possible sample stimuli (two or four) and the number of possible comparison stimuli (two or four) factorially across groups. Birds in all four groups were initially trained on a zero-delay, conditional discrimination with lines (vertical and horizontal) and/or shapes (circle and triangle), and were then tested with longer delays between sample offset and comparison onset. Acquisition of the conditional discrimination was affected by both the number of sample and comparison stimuli: birds were slower to reach criterion the greater the number in either stimulus set. During delay testing, however, only the number of comparisons affected performance. Overall, retention was poorer with four comparisons than with two. These data provide evidence for prospective coding in pigeon short-term memory.     

Dual-task automatization: The key role of sensory–motor modality compatibility

How do people automatize their dual-task performance through bottleneck bypassing (i.e., accomplish parallel processing of the central stages of two tasks)? In the present work we addressed this question, evaluating the impact of sensory–motor modality compatibility—the similarity in modality between the stimulus and the consequences of the response. We hypothesized that incompatible sensory–motor modalities (e.g., visual–vocal) create conflicts within modality-specific working memory subsystems, and therefore predicted that tasks producing such conflicts would be performed less automatically after practice. To probe for automaticity, we used a transfer psychological refractory period (PRP) procedure: Participants were first trained on a visual task (Exp. 1) or an auditory task (Exp. 2) by itself, which was later presented as Task 2, along with an unpracticed Task 1. The Task 1–Task 2 sensory–motor modality pairings were either compatible (visual–manual and auditory–vocal) or incompatible (visual–vocal and auditory–manual). In both experiments we found converging indicators of bottleneck bypassing (small dual-task interference and a high rate of response reversals) for compatible sensory–motor modalities, but indicators of bottlenecking (large dual-task interference and few response reversals) for incompatible sensory–motor modalities. Relatedly, the proportion of individuals able to bypass the bottleneck was high for compatible modalities but very low for incompatible modalities. We propose that dual-task automatization is within reach when the tasks rely on codes that do not compete within a working memory subsystem.

     

Saved by a log: how do humans perform hybrid visual and memory search?

Could you find 1 of your 1,000 Facebook friends in a crowd of 100? Even at a rate of 25 ms per comparison, determining that no friends were in the crowd would take more than 40 min if memory and visual search interacted linearly. In the experiment reported here, observers memorized pictures of 1 to 100 targets and then searched for any of these targets in visual displays of 1 to 16 objects. Response times varied linearly with visual set size but logarithmically with memory set size. Data from memory set sizes of 1 through 16 accurately predicted response times for different observers holding 100 objects in memory. The results would be consistent with a binary coding of visual objects in memory and are relevant to applied searches in which experts look for any of many items of interest (e.g., a radiologist running through a mental checklist of what might be wrong in a car-crash victim or an airport screener looking for any of a list of prohibited items in a carry-on bag).     

A Simon effect in memory retrieval: Evidence for the response-discrimination account

According to the traditional view, the effects of irrelevant stimulus location on the selection of a spatial response to a nonspatial stimulus feature (Simon effect) result from long-term associations between spatial stimulus codes and spatially corresponding response codes. According to an alternative view, the response-discrimination account, Simon effects arise from interactions between spatial stimulus codes and response labels in working memory (WM). The latter account predicts Simon effects when participants use spatial labels for response representation in WM, even when the actual responses have no spatial features (e.g., saying the word "plate"). The prediction was tested in an experiment, in which participants first encoded two words at different locations, and then responded to a stimulus by saying the word from the location indicated by stimulus color. The manipulation concerned the correspondence between irrelevant location of the colored stimulus and the retrieval cue for the vocal responses (i.e., word location in the encoding display). A Simon effect in memory retrieval was observed, supporting the response-discrimination account.     

A comparison of stimulus set size on tact training for children with autism spectrum disorder

Previous studies on skill acquisition have taught targets in stimulus sets composed of different numbers of stimuli. Although the rationale for selection of a stimulus set size is not clear, the number of target stimuli trained within a set is a treatment decision for which there is limited empirical support. The current investigation compared the efficiency of tact training in 4 stimulus set sizes, each of which included 12 stimuli grouped into (a) 4 sets of 3 stimuli, (b) 3 sets of 4 stimuli, (c) 2 sets of 6 stimuli, and (d) 1 set of 12 stimuli. Results of all 4 participants with autism spectrum disorder show tact training with larger (i.e., 6 and 12) stimulus set sizes was more efficient than training with smaller (i.e., 3 and 4) stimulus set sizes.     

Adolescents' performance on the Iowa Gambling Task: implications for the development of decision making and ventromedial prefrontal cortex

Healthy adolescents (79 girls, 66 boys), ages 9-17, completed the Iowa Gambling Task (IGT; A. Bechara, A. R. Damasio, H. Damasio, & S. W. Anderson, 1994) as well as working memory (digit span) and behavioral inhibition (go/no-go) tasks. Cross-sectional age-related changes were seen on all 3 tasks. Gender differences were seen in IGT deck preference and attentional variables (i.e., go/no-go hit rate and forward digit span). After age, gender, and general intellectual abilities were controlled for, IGT performance was not predicted by working memory or behavioral inhibition scores. Findings suggest that the ventromedial prefrontal cortex or its connections are functionally maturing during adolescence in a manner that can be distinguished from maturation of other prefrontal regions. Development of these functions may continue into young adulthood.     

Visual working memory enhances target discrimination accuracy with single-item displays

The maintenance of information in visual working memory has been shown to bias the concurrent processing in favor of matching visual input. The present study aimed to examine whether this bias can act at an early stage of processing to enhance target feature perception in single-item displays. Participants were sequentially presented with two distinct colored stimuli as memory samples and a retro-cue indicating which of the two samples should be maintained for subsequent memory test. During the retention interval, they had to discriminate the gap orientation of a Landolt target presented through a single visual stimulus that could match one or neither of the two samples. Across two experiments, we consistently found that discrimination performance was more accurate when the Landolt target was situated within a stimulus that matched the sample being retained in visual working memory, as compared with when the target was not. This effect cannot be attributed to the mechanism of passive priming, because we failed to observe priming effects when the stimulus containing the target matched the sample that was retro-cued to be irrelevant to the working memory task, as compared to when the stimulus matched neither sample. Given the fact that target stimuli were presented in single-item displays wherein external noise was precluded, the present findings demonstrate that the working memory bias of visual attention operating in the absence of stimulus competition facilitates early perceptual processing at the attended location via signal enhancement.

     

Set-specific capture can be reduced by preemptively occupying a limited-capacity focus of attention

Recent work has shown that contingent attentional capture effects can be especially large when multiple attentional sets for color guide visual search (Moore & Weissman, 2010). In particular, this research suggests that detecting a target-colored (e.g., orange) distractor leads the corresponding attentional set (e.g., identify orange letters) to enter a limited-capacity focus of attention in working memory, where it remains briefly while the distractor is being attended. Consequently, the ability to identify a differently-colored (e.g., green) target 100-300 ms later is impaired because the appropriate set (e.g., identify green letters) cannot also enter the focus of attention. In two experiments, we investigated whether such set-specific capture can be reduced by preemptively occupying the focus of attention. As predicted, a target-colored central distractor presented 233 ms before a target-colored peripheral distractor eliminated set-specific capture arising from the peripheral distractor. Moreover, this effect was observed only when the central distractor's color (e.g., orange) (a) matched a different set than the upcoming peripheral distractor's color (e.g., green) and (b) matched the same set as the upcoming central target's color (e.g., orange). We conclude that the same working memory limitations that give rise to set-specific capture can be preemptively exploited to reduce it.     

Scheduling Processes in Working Memory: Instructions Control the Order of Memory Search and Mental Arithmetic

Humans must often use working memory to execute processes one at a time because of its limited capacity. Two experiments tested where limits in access to working memory occur. Subjects searched a short-term memory set for one stimulus digit and performed mental arithmetic with another stimulus digit. In one experiment, they were told to carry out the mental arithmetic before the memory search and to make the arithmetic response first. In the other, they were instructed to perform the tasks in the opposite order. The overt responses were executed in the prescribed order. Moreover, the covert working memory processes were executed in the prescribed order, as revealed by a critical path network analysis of reaction times. Results are explained in terms of a double-bottleneck model in which central processes and responses are constrained to be carried out for one task at a time.     

Comparison of the effects of scopolamine administered before and after acquisition in a test of visual recognition memory in monkeys

The effect of scopolamine on visual recognition memory in rhesus monkeys was assessed with a delayed nonmatching-to-sample task employing trial-unique stimuli. During the acquisition phase, 40 sample stimuli were presented sequentially. During the test phase, these same stimuli were presented in the reverse order, each paired with a novel stimulus. The animal was rewarded for choosing the novel stimulus in each pair. Two versions of this design were used. In Task 1, scopolamine (10.0 or 17.8 micrograms/kg) was administered 20 min prior to acquisition, which was followed immediately by the test phase. In Task 2, the drug was administered immediately after acquisition, which was followed 20 min later by the test phase. Performance was impaired in a dose-related manner in Task 1, but not at all in Task 2, indicating that the effects of scopolamine on performance cannot be attributed to an impairment either in the retrieval of stored information or in the attentive or perceptual discriminative processes needed for such retrieval, or, by implication, for storage. In addition, the forgetting curves for scopolamine in Task 1 were parallel to those of the control sessions; i.e., the curves did not diverge with increasing delay intervals, indicating that scopolamine did not increase the rate of forgetting. Taken together, the results suggest that scopolamine interferes selectively with the initial storage of the information to be remembered.     

Working memory can enhance unconscious visual perception

We demonstrate that unconscious processing of a stimulus property can be enhanced when there is a match between the contents of working memory and the stimulus presented in the visual field. Participants first held a cue (a colored circle) in working memory and then searched for a brief masked target shape presented simultaneously with a distractor shape. When participants reported having no awareness of the target shape at all, search performance was more accurate in the valid condition, where the target matched the cue in color, than in the neutral condition, where the target mismatched the cue. This effect cannot be attributed to bottom-up perceptual priming from the presentation of a memory cue, because unconscious perception was not enhanced when the cue was merely perceptually identified but not actively held in working memory. These findings suggest that reentrant feedback from the contents of working memory modulates unconscious visual perception.     

Guided search through memory

In “hybrid” search, observers search a visual display for any of several targets held in memory. It is known that the contents of the memory set can guide visual search (e.g., if the memorized targets are all animals, visual attention can be guided away from signs). It is not known if the visual display can guide memory search (e.g., if the memory set is composed of signs and animals, can a visual display of signs restrict memory search to just the signs?). In three hybrid search experiments, participants memorized sets of items that belonged to either one or several categories. Participants were then presented with visual displays containing multiple items, also drawn from one or several categories. Participants were asked to determine if any of the items from their current memory set were present in the visual display. We replicate the finding that visual search can be guided by the contents of memory. We find weaker, novel evidence that memory search can be guided by the contents of the visual display.     

Automatic and directed search processes in solving simple semantic-memory problems

The cognitive processes involved in simple semantic-memory problems were investigated in four experiments. On each trial of Experiments 1 and 2, two stimulus words were presented, with the instructions to find a third word (i.e., the solution) that, when coupled with each of the stimuli, would yield two word pairs used in everyday language (e.g., surprise and birthday, for which the solution is party). The results of the two experiments indicated that informing the subject whether the solution constituted the first or the second element in the word pairs facilitated both likelihood and speed of solution attainment. In addition, solution attainment was relatively high for items based on frequently used word pairs (Experiment 1) and for items in which the stimuli appear, in everyday language, in a small number of word pairs (Experiment 2). In Experiment 3, the subjects were required to produce word pairs containing one of the two stimulus words from the items used in Experiment 2. Solution production was facilitated by rehearsing the second stimulus word of the specific item. The conclusion, supported by a post hoc analysis of the results of Experiments 2 and 3 (Experiment 4), was that indirect priming from one stimulus word may facilitate solution production from a searched word. These results are interpreted in terms of automatic and controlled processes, and their relevance to two different models for retrieval from semantic memory is discussed.     

Performance dissociation during verbal and spatial working memory tasks

Past research has inconsistently distinguished the neural substrates of various types of working memory. Task design and individual performance differences are known to alter patterns of brain response during working-memory tasks. These task and individual differences may have produced discrepancies in imaging findings. This study of 50 healthy adults (M(age) = 19.6 yr., SD = .8) examined performance during various parametric manipulations of a verbal and spatial n-back working-memory task. Performance systematically dissociated on the basis of working-memory load, working memory type, and stimulus difficulty, with participants having greater accuracy but slower response time during conditions requiring verbal versus spatial working memory. These findings hold implications for cognitive and neuroimaging studies of verbal and spatial working memory and highlight the importance of considering both task design and individual behavior.     

Working memory dependence of spatial contextual cueing for visual search

When spatial stimulus configurations repeat in visual search, a search facilitation, resulting in shorter search times, can be observed that is due to incidental learning. This contextual cueing effect appears to be rather implicit, uncorrelated with observers’ explicit memory of display configurations. Nevertheless, as I review here, this search facilitation due to contextual cueing depends on visuospatial working memory resources, and it disappears when visuospatial working memory is loaded by a concurrent delayed match to sample task. However, the search facilitation immediately recovers for displays learnt under visuospatial working memory load when this load is removed in a subsequent test phase. Thus, latent learning of visuospatial configurations does not depend on visuospatial working memory, but the expression of learning, as memory‐guided search in repeated displays, does. This working memory dependence has also consequences for visual search with foveal vision loss, where top‐down controlled visual exploration strategies pose high demands on visuospatial working memory, in this way interfering with memory‐guided search in repeated displays. Converging evidence for the contribution of working memory to contextual cueing comes from neuroimaging data demonstrating that distinct cortical areas along the intraparietal sulcus as well as more ventral parieto‐occipital cortex are jointly activated by visual working memory and contextual cueing.     

Emotion-induced amnesia in rats: working memory-specific impairment, corticosterone-memory correlation, and fear versus arousal effects on memory

We have shown previously that psychological stress (predator exposure) impairs spatial memory in rats. We have extended that finding here to show that predator stress selectively impaired recently acquired (hippocampal-dependent) spatial working memory without affecting long-term (hippocampal-independent) spatial reference memory. We also investigated why predator exposure impairs memory. Was spatial memory impaired because of the fear-provoking aspects of predator exposure or only because the cat was a novel and arousing stimulus? If the latter possibility was correct, then any novel and arousing stimulus, independent of its emotional valence (i.e., aversive or appetitive), would impair memory. We found that spatial working memory was not impaired when the male rats were exposed to a sexually receptive female rat, a stimulus that was novel and arousing to them, but not aversive. We also found that there was an equivalent increase in serum corticosterone levels in male rats exposed to either a cat or a female rat, but only the cat-exposed rats exhibited a significant correlation between corticosterone levels and impaired memory. Overall, this series of experiments demonstrates that (1). predator stress selectively impaired working (hippocampal-dependent), but not reference (hippocampal-independent), memory; (2). a fear-provoking stimulus, and not merely novelty and increased arousal, impaired spatial memory; and (3). increased corticosterone levels correlated with impaired spatial working memory only under predator exposure, that is, fear-provoking conditions.     

ArduiPod Box: A low-cost and open-source Skinner box using an iPod Touch and an Arduino microcontroller

This article introduces the ArduiPod Box, an open-source device built using two main components (i.e., an iPod Touch and an Arduino microcontroller), developed as a low-cost alternative to the standard operant conditioning chamber, or “Skinner box.” Because of its affordability, the ArduiPod Box provides an opportunity for educational institutions with small budgets seeking to set up animal laboratories for research and instructional purposes. A pilot experiment is also presented, which shows that the ArduiPod Box, in spite of its extraordinary simplicity, can be effectively used to study animal learning and behavior.