Memory Set Items Research Articles

Searching while loaded: Visual working memory does not interfere with hybrid search efficiency but hybrid search uses working memory capacity.

In "hybrid search" tasks, such as finding items on a grocery list, one must search the scene for targets while also searching the list in memory. How is the representation of a visual item compared with the representations of items in the memory set? Predominant theories would propose a role for visual working memory (VWM) either as the site of the comparison or as a conduit between visual and memory systems. In seven experiments, we loaded VWM in different ways and found little or no effect on hybrid search performance. However, the presence of a hybrid search task did reduce the measured capacity of VWM by a constant amount regardless of the size of the memory or visual sets. These data are broadly consistent with an account in which VWM must dedicate a fixed amount of its capacity to passing visual representations to long-term memory for comparison to the items in the memory set. The data cast doubt on models in which the search template resides in VWM or where memory set item representations are moved from LTM through VWM to earlier areas for comparison to visual items.

Brain oscillatory 1–30 Hz EEG ERD/ERS responses during the different stages of an auditory memory search task

Event-related desynchronization (ERD) and event-related synchronization (ERS) responses of 1–30 Hz EEG frequencies during the different stages of an auditory Sternberg memory task were examined. The ERD/ERS responses were examined separately for successive memory set items (four) and for the two recognition conditions (YES/NO). The presentation of the memory set elicited ERS responses in the theta and alpha frequencies, and also beta ERD responses. These ERD/ERS responses elicited during encoding were found to evolve with successive memory set item presentation. The ERD/ERS responses elicited during the presentation of the probe dissociated significantly between the two recognition conditions (YES/NO). When the probe was included in the memory set (YES condition), recognition elicited stronger alpha and beta frequency ERD responses as compared to the NO condition. The findings from the current study verify that alpha ERD/ERS responses robustly dissociate between auditory encoding and recognition. The increasing alpha ERS responses with increasing memory set item presentation during encoding may be correlates of the functioning phonological loop, active memory maintenance and/or attention. The alpha ERD responses during recognition are undoubtedly associated with auditory memory search processes and distinguish between previously presented versus not presented verbal material. We propose that alpha ERD/ERS responses reflect explicitly auditory memory processes, discriminating between auditory encoding and recognition. Theta ERS responses may be associated with working memory processes, and possibly more specifically with the functioning of the central executive. Beta ERD/ERS responses may reflect also cognitive and/or memory processing, rather than merely the activity of the motor cortices.

Multiple Interference Effects in Short-Term Recognition Memory

Five experiments, using a probe recognition procedure, examined the codes involved in short-term memory. Interference effects were obtained for probes with an orthographic, associative, or semantic relationship to a memory set item. The orthographic interference effects appeared to result from matches on the basis of abstract letter codes (i.e., graphemes) rather than overlap of visual features. The associative and semantic effects differed from what might be predicted on the basis of spreading activation, suggesting that these effects are qualitatively different from semantic priming effects observed in lexical decision tasks. These results support models of short-term memory in which items are represented as groups of features and recognition depends on a comparison of the features of the probe to those of the memory set items.

Hearing-impaired perceivers’ encoding and retrieval speeds for auditory, visual, and audiovisual spoken words

Perceptual encoding and memory retrieval processing speeds were assessed for spoken words in 26 subjects, mean age 66, with mild to moderate acquired sensorineural hearing loss. Subjects were trained to achieve error-free recognition of a set of ten spoken words in auditory, visual (speech reading), and audiovisual conditions. They then performed the Sternberg item recognition task in each of the modality conditions using the same set of ten words. The task involved presenting memory sets of one to four words, followed by a probe word to which subjects made a speeded ‘‘YES’’ or ‘‘NO’’ button response to indicate whether the probe matched any of the memory set items. Least-squares linear models provided good fits to subjects’ memory-set size by reaction time functions (mean r2>0.90 for all three conditions). Using the models’ intercepts and slopes to represent encoding and retrieval times, respectively, Wilcoxon tests showed significant differences among the conditions with respect to both encoding and retrieval speed, with audiovisual fastest and visual slowest. These results are interpreted as evidence for: (1) audiovisual ‘‘benefit’’ to processing speed in hearing-impaired speech perception; (2) relativeinefficiency of encoding visual speech; and (3) representation differences associated with the modalities. [Work supported by NIH-NIDCD.]

Allocation of attentional resources during habituation to food cues.

Two experiments were designed to test the hypothesis that habituation to repeated food cues can be inhibited by allocating processing resources to nonfood cues. In two experiments, the salivary response to 10 presentations of lemon yogurt was assessed while subjects engaged in a controlled cognitive search task (demanding attentional resources), an automatic search task (needing fewer attentional resources), or no task. In Experiment 1, the controlled and automatic search tasks differed in the number of memory set items. In Experiment 2, the size of the memory sets was held constant, and individuals were provided practice to stabilize the different search strategies in the task. The automatic search and no task groups habituated to the repeated presentation of food cues in both experiments, but the controlled search group did not. These results support the hypothesis that allocation of attentional resources to external cues can influence the processing of food cues.

Prefrontal and posterior cortical activation during auditory working memory

The present study investigated brain mechanisms underlying auditory memory. In a modified Sternberg memory scanning task, 11 subjects indicated whether a probe sound was part of a previously presented 4-item memory set by a button press. Behaviorally, subjects responded fastest and most accurately to probes that matched the last memory set items and slowest and least accurately to negative probes and to positive probes to the first two memory set items. Electrophysiologically, probes to the last memory set items elicited the largest amplitude and earliest latency P3 components while other probes elicited smaller amplitude, prolonged P3s as well as a negativity around 400 ms. These results suggest that subjects utilized a trace strength/self-terminating search model to perform the memory scanning task. Subjects only generated the P3 component during the matching phase of the auditory memory task while a sustained frontal negativity was elicited during both the encoding and matching phase. Taken together these findings provide evidence of differential activation of distributed neural activity during non-linguistic auditory memory.

Event Related Potentials and Serial List Picture Memory in Parkinson’s Patients

Two experiments examined short-term memory for order information in six patients diagnosed with Parkinson's disease (PD) and six control subjects while event related potentials (ERPs) were recorded. The subjects were tested for recognition of abstract spatial designs and words after a 5 s retention interval. The PD patients failed to respond in 29% of all trials, but the overall accuracy was similar to that in the control group when these trials were excluded. The corresponding ERP results show serial position variations both after presentation of the probe items, and after presentation of the memory set items. The amplitudes were generally lower at all positions for the PD patients at the parietal midline electrode, and the amplitudes were similar for both groups at the frontal electrode. Also, the ERP latencies were significantly slower for the PD patients than for the control group at all conditions. Indirectly the data are consistent with an interpretation of cognitive deficit in PD stressing attention resources.

Event related potentials and serial list picture memory in Parkinson's patients.

Two experiments examined short-term memory for order information in six patients diagnosed with Parkinson's disease (PD) and six control subjects while event related potentials (ERPs) were recorded. The subjects were tested for recognition of abstract spatial designs and words after a 5 s retention interval. The PD patients failed to respond in 29% of all trials, but the overall accuracy was similar to that in the control group when these trials were excluded. The corresponding ERP results show serial position variations both after presentation of the probe items, and after presentation of the memory set items. The amplitudes were generally lower at all positions for the PD patients at the parietal midline electrode, and the amplitudes were similar for both groups at the frontal electrode. Also, the ERP latencies were significantly slower for the PD patients than for the control group at all conditions. Indirectly the data are consistent with an interpretation of cognitive deficit in PD stressing attention resources.

Response Time Distributions in Memory Scanning

This article reports the results of a memory scanning experiment (S. Sternberg. 1966, Science, 153, 652-654) in which each of four subjects participated in about 1500 experimental trials per memory set size. These large samples made it possible to test a number of important nonparametric (i.e., model-free) properties of the response time (RT) distributions. These properties place severe constraints on the various memory scanning models and they provide a deeper description of the data than summary statistics or goodness-of-fit values. Five conclusions stood out. First, increasing the size of the memory set induced the strongest possible form of stochastic dominance on both target present and target absent trials. Second, the RT hazard functions were nonmonotonic, thereby falsifying a large class of serial searell models, Third, strong evidence was obtained against art exhaustive search. Fourth, some evidence was found that adding an item to the memory set inserts a stage with exponentially distributed duration into the processing claim, at least on largest absent trials. Fifth, the data supported the hypothesis that three of the subjects stored the representations of the memory set items in a visual short-term memory system and the fourth subject used all acoustic short-term system. To our knowledge, the only extant model of memory scanning that is consistent with all these results assumes that search is parallel, self-terminating, and of very limited capacity.

Adult age differences in attentional allocation during memory search.

Young and older adults performed a memory search task in which, before probe onset, a cue indicated which of 4 memory-set items the probe was most likely to be. The results were consistent with an attentional allocation model in which performance represents a weighted combination, across trials, of focused (i.e., selective) versus distributed attention. The model significantly underestimated the reaction time required by miscued trials, probably because of the response inhibition occurring on these trials. The degree to which Ss relied on focused attention was significantly greater for older adults than for young adults. The estimated time required to shift attention between memory-set items was equivalent for the 2 age groups.

Event-related potential correlates of the serial position effect in short-term memory

Event-related potential (ERP) correlates of the serial position effect in short-term memory were investigated using a memory scanning task. Nine normal young adults (18–39 years) indicated whether a probe item was a member of a previously presented 5-item memory set by pressing 1 of 2 reaction-time buttons. Three types of stimuli were used: verbal digits presented both auditorily and visually, and musical notes presented auditorily. The ERPs to the probes were separately averaged according to the serial position of the probe (1, 2, 3, 4, or 5) in the memory set. The ERPs to the memory set items in positions 1, 3 and 5 also were separately averaged. Both baseline-to-peak and average amplitudes of a late positive parietal potential to the probes were larger to probe items presented in the last position in the memory set than to probes presented in the middle positions (2, 3 and 4), showing a significant recency effect, but only for auditory digits. Reaction time reflected significant recency effects for both auditory digits and notes, but not for visual digits. Response accuracy (percent correct) showed a significant recency effect only for notes. For each stimulus type, both the baseline-to-peak and average amplitudes of a late frontal component to the memory set items became more negative (in the case of the visual digits, less positive) in the third and last serial position of the memory set compared to the first. These findings provide electrophysiological evidence of serial position effects in short-term memory, which, during memory scanning, are dependent on stimulus modality (auditory, visual) and type (verbal, non-verbal).

The effects of practice and task structure on components of the event-related brain potential.

ABSTRACTThe present study focused on the effects of, and the interactions between, practice and task structure on human performance. The development of automatic processing through consistent stimulus‐response mapping (CM) was assessed by means of measures of reaction time and event‐related brain potentials. The subjects performed a visual search task in which they responded by pressing a button whenever a probe matched a memory set item. The variables manipulated in the study included the number of memory set items (1 or 4), the task structure (CM or VM), and the probability of occurrence of a memory set item (.2 or .8). Set size had a significant effect on RT in both CM and VM conditions prior to practice and in the VM condition following extensive practice. P300 latency mirrored RT, suggesting that the development of automatic processing substantially reduced stimulus evaluation time. The commonly observed relationship between probability and P300 amplitude, with larger P300s elicited by infrequent events, was found in the VM conditions but not in the CM condition after practice. Two different negative components were affected by stimulus mismatch. The N200 component behaved in a similar manner during automatic and controlled processing. However, a late frontally negative component was sensitive to the degree of mismatch only during controlled processing.

Memory search and visual spatial attention: An event-related brain potential analysis

Event-related brain potentials (ERPs) were recorded from subjects as they attended to one diagonal of a visual display. The task was to respond only to memory set items (targets) at the attended diagonal and to ignore stimuli at the other diagonal. The probability that the display contained either an attended or an unattended target was 0.30. The spatial separation between attended and unattended stimuli was 1.6°. The ERP elicited by stimuli at the unattended diagonal contained a sequence of phasic components. The early N 170 and P 250 components were elicited by the onset of the display and the later components N 480 and P 550 by the offset of the display. The presence of masks delayed N 170 and P 250. The ERPs elicited by attended non-targets, in addition, contained an increased N 350 (C z, F z) and P 410 (P 3a, P z, C z). The ERPs elicited by attended and unattended non-targets started to differ after 200 msec. This finding suggested that selection is relatively late if selection must be based on a conjunction of features (location and orientation) and if the spatial separation between attended and unattended stimuli is small. Memory-set size affected the ERPs after 250 msec. The ERPs elicited by attended stimuli contained a broadly distributed (F z, C z, P z) negative endogeneous component. The amplitude of this component was related to memory-set size. Finally, the ERPs elicited by attended targets contained a large P 3b (P z, O z) with a peak latency around 600 msec. The ERP results suggested the existence of three processing stages: (1) orienting to the attended stimuli; (2) controlled search, and (3) target decision.

Order effect in recognition latency for multiple-item probes.

A strong order effect in response latency has been found in recognition experiments with varied memory sets and multiple item probes, in which all items must be positive for a positive response. In this article, three experiments are reported that support the idea that incidental order information may be stored in the form of combination items derived from subjective grouping of memory set items. Thus, the memory set of six items, ABCDEF, may be subjectively grouped into two combination items ABC and DEF. The key evidence supporting the combination item hypothesis and subjective item grouping was that prominent order effects exist if probe items are all within a subjective group but that such effects are small if the probe is between-groups. Experiment 1 used visually degraded probes and found serial position effects but no decrease of the order effect with degradation. Experiment 2 tested whether combination items are likely to be encoded in auditory-articulatory form and thus persist for several seconds, by using interpolated intervals of up to 30 s. The order effect was found to persist at the end positions of the memory set but to decrease considerably at intermediate positions. Experiment 3 provided a test of subjective item grouping and demonstrated the dominance of three-item subjective groups. A model based on item matching strength as a function of position within a group is briefly outlined.

Cerebral Asymmetries in Processing Proper Names: Evidence of an Efficiency Difference

An investigation of the capacities of the cerebral hemispheres to process proper names was conducted using a memory-scanning paradigm. The results indicated that rate at which the test name was compared against the memory set items varied with the visual half-field stimulated. This is interpreted as indicating that both hemispheres employed the same comparison process but that the left hemisphere was more efficient, reflecting a quantitative hemisphere asymmetry.

Different predictors of memory scanning with unidimensional and digit stimuli

The processing of digit and unidimensional brightness stimuli was examined in the traditional Sternberg fixed-set paradigm. From a total set size of 10, 18 different memory sets were studied, 6 each at memory set sizes of 1, 2, and 3. Three different variables, which are in general correlated, were used to predict performance: memory set size (M), a measure based on inferred distance relationships among the stimuli constituting the positive and negative sets (d), and a measure based on the number of inferred “decision boundaries” necessary to separate all memory set items from the items remaining in the set (DB). For the digit stimuli the results were consistent with previous research, and memory set size was the prepotent predictor. For the unidimensional brightnesses, DB was the prepotent predictor, and choice reaction times (CRTs) to both positive and negative probes were a function of the distance of the probe item from the closest member of the complementary set. However, for the digit stimuli this was found only for negative probes; CRTs to positive digit probes were independent of the distance from the closest negative set member.

Recency, immediate recognition memory, and reaction time

Four classes of possible mechanisms for short-term item recognition are distinguished: (I) pure list-search, (II) direct-access activation (or trace strength) discrimination, (III) mixtures (of I and II), and (IV) response-association. Manipulations of recency, particularly of negative probe items, provide critical tests between them. Two experiments are reported using Sternberg' s 1966 varied-set reaction time paradigm, coupled with procedures intended to minimize rehearsal and control the recency of probes and memory set items. RT and error rate were greater for negative probe items that had recently been presented than for items less recently presented, and this effect increased with positive set size. In contrast, positive RT was, except for the initial item, a decreasing function of recency (= serial position), and there was no additional effect of set size per se. A brief filled delay between list and probe increased positive RT but not the slope of the set size function. These and other findings appear to reject models of Classes I and IV and, while implying some direct discrimination of an item's recency, require modification of the models of Classes II and III. The implications are discussed with respect to the relation between the two versions of Sternberg's paradigm and also in connection with facilitatory “priming” effects in memory.

Memory search processes for words and pictures in elementary school children

Children in the fourth and sixth grades searched memory sets of two, three, or four items for the presence of a given word or picture probe. The memory sets were all of one form on any trial, being either words or easily nameable pictures, and the probe form was varied to match or mismatch the form of the memory items. Subjects responded more rapidly when the probe form and memory set form matched, an effect that did not interact with the number of memory set items. Presumably, stimulus form effects are limited to encoding processes which precede comparisons between the probe and memory set items. The comparison process itself appears to be independent of the form in which the probe is presented.