Neural evidence of switch processes during semantic and phonetic foraging in human memory.

Humans may retrieve words from memory by exploring and exploiting in "semantic space" similar to how nonhuman animals forage for resources in physical space. This has been studied using the verbal fluency test (VFT), in which participants generate words belonging to a semantic or phonetic category in a limited time. People produce bursts of related items during VFT, referred to as "clustering" and "switching." The strategic foraging model posits that cognitive search behavior is guided by a monitoring process which detects relevant declines in performance and then triggers the searcher to seek a new patch or cluster in memory after the current patch has been depleted. An alternative body of research proposes that this behavior can be explained by an undirected rather than strategic search process, such as random walks with or without random jumps to new parts of semantic space. This study contributes to this theoretical debate by testing for neural evidence of strategically timed switches during memory search. Thirty participants performed category and letter VFT during functional MRI. Responses were classified as cluster or switch events based on computational metrics of similarity and participant evaluations. Results showed greater hippocampal and posterior cerebellar activation during switching than clustering, even while controlling for interresponse times and linguistic distance. Furthermore, these regions exhibited ramping activity which increased during within-patch search leading up to switches. Findings support the strategic foraging model, clarifying how neural switch processes may guide memory search in a manner akin to foraging in patchy spatial environments.

Improving Memory Search Through Model-Based Cue Selection.

We often use cues from our environment when we get stuck searching our memories, but prior research has failed to show benefits of cuing with other, randomly selected list items during memory search. What accounts for this discrepancy? We proposed that cues' content critically determines their effectiveness and sought to select the right cues by building a computational model of how cues affect memory search. Participants (N = 195 young adults from the United States) recalled significantly more items when receiving our model's best (vs. worst) cue. Our model provides an account of why some cues better aid recall: Effective cues activate contexts most similar to the remaining items' contexts, facilitating recall in an unsearched area of memory. We discuss our contributions in relation to prominent theories about the effect of external cues.

Evidence That Event Boundaries Are Access Points for Memory Retrieval.

When recalling memories, we often scan information-rich continuous episodes, for example, to find our keys. How does our brain access and search through those memories? We suggest that high-level structure, marked by event boundaries, guides us through this process: In our computational model, memory scanning is sped up by skipping ahead to the next event boundary upon reaching a decision threshold. In adult Mechanical Turk workers from the United States, we used a movie (normed for event boundaries; Study 1, N = 203) to prompt memory scanning of movie segments for answers (Study 2, N = 298) and mental simulation (Study 3, N = 100) of these segments. Confirming model predictions, we found that memory-scanning times varied as a function of the number of event boundaries within a segment and the distance of the search target to the previous boundary (the key diagnostic parameter). Mental simulation times were also described by a skipping process with a higher skipping threshold than memory scanning. These findings identify event boundaries as access points to memory.

forager: a Python package and web interface for modeling mental search.

Analyzing data from the verbal fluency task (e.g., "name all the animals you can in a minute") is of interest to both memory researchers and clinicians due to its broader implications for memory search and retrieval. Recent work has proposed several computational models to examine nuanced differences in search behavior, which can provide insights into the mechanisms underlying memory search. A prominent account of memory search within the fluency task was proposed by Hills et al. (2012), where mental search is modeled after how animals forage for food in physical space. Despite the broad potential utility of these models to scientists and clinicians, there is currently no open-source program to apply and compare existing foraging models or clustering algorithms without extensive, often redundant programming. To remove this barrier to studying search patterns in the fluency task, we created forager, a Python package ( https://github.com/thelexiconlab/forager ) and web interface ( https://forager.research.bowdoin.edu/ ). forager provides multiple automated methods to designate clusters and switches within a fluency list, implements a novel set of computational models that can examine the influence of multiple lexical sources (semantic, phonological, and frequency) on memory search using semantic embeddings, and also enables researchers to evaluate relative model performance at the individual and group level. The package and web interface cater to users with various levels of programming experience. In this work, we introduce forager's basic functionality and use cases that demonstrate its utility with pre-existing behavioral and clinical data sets of the semantic fluency task.

The impact of cognitive load on prospective and retrospective time estimates at long durations: An investigation using a visual and memory search paradigm.

As human beings, we are bound by time. It is essential for daily functioning, and yet our ability to keep track of time is influenced by a myriad of factors (Block & Zakay, 1997, Psychonomic Bulletin & Review, 4[2], 184-197). First and foremost, time estimation has been found to depend on whether participants estimate the time prospectively or retrospectively (Hicks et al., 1976, The American Journal of Psychology, 89[4], 719-730). However, there is a paucity of research investigating differences between these two conditions in tasks over two minutes (Tobin et al., 2010, PLOS ONE, 5[2], Article e9271). Moreover, estimates have also been shown to be influenced by cognitive load. We thus investigated participants' ability to keep track of time during a visual and memory search task and manipulated its difficulty and duration. Two hundred and ninety-two participants performed the task for 8 or 58 minutes. Participants in the prospective time judgment condition were forewarned of an impending time estimate, whereas participants in the retrospective condition were not. Cognitive load was manipulated and assessed by altering the task's difficulty. The results revealed a higher overestimation of time in the prospective condition compared with the retrospective condition. However, this was found in the 8-minute task only. Overall, participants significantly overestimated the duration of the 8-minute task and underestimated the 58-minute task. Finally, cognitive load had no effect on participants' time estimates. Thus, the well-known cross-over interaction between cognitive load and estimation paradigm (Block et al., 2010, Acta Psychologica, 134[3], 330-343) did not extend to a longer duration in this experiment.

Computational Models of Memory Search.

The capacity to search memory for events learned in a particular context stands as one of the most remarkable feats of the human brain. How is memory search accomplished? First, I review the central ideas investigated by theorists developing models of memory. Then, I review select benchmark findings concerning memory search and analyze two influential computational approaches to modeling memory search: dual-store theory and retrieved context theory. Finally, I discuss the key theoretical ideas that have emerged from these modeling studies and the open questions that need to be answered by future research.

Epistemic Responsibility - Labored, Loosened, and Lost: Staging Alzheimer's Disease.

Interlocutors hold one another accountable for knowing certain information about themselves (their roles, activities, and memories) and for keeping track of information in the current conversational exchange. When speakers have trouble with this expectation, they themselves work to repair the breach, often doing a memory search, or when unsuccessful they provide an account (e.g. "I don't remember"). Memory searches (like word searches) are observable, interactional accomplishments. Speakers disengage with their interlocutors (look away), produce hesitation markers, take repeated pauses, engage in pre-positioned and post-positioned repairs, make epistemic assessments, and on finding an answer, re-engage with their interlocutors (look back). For their part, interlocutors comply with the search by not interrupting and continuing to yield the floor. At progressively severe stages of Alzheimer's disease, individuals exhibit increasingly labored memory searches that often trail off into non-answers, until at the latest stages, they eschew the search and (almost smoothly) provide either grammatically appropriate but wrong and improbable answers or give answers to previous questions on now closed topics. With data from the clinical administration of a disease staging instrument (Clinical Dementia Rating) this article examines the inexorable loss of epistemic responsibility as a key discursive dynamic in the progression of the disease.

Item frequency in probe-recognition memory search: Converging evidence for a role of item-response learning.

In short-term probe-recognition tasks, observers make speeded old-new recognition judgments for items that are members of short lists. However, long-term memory (LTM) for items from previous lists influences current-list performance. The current experiment pursued the nature of these long-term influences-in particular, whether they emerged from item-familiarity or item-response-learning mechanisms. Subjects engaged in varied-mapping (VM) and consistent-mapping (CM) short-term probe-recognition tasks (e.g., Schneider & Shiffrin, Psychological Review, 84, 1-66, 1977). The key manipulation was to vary the frequency with which individual items were presented across trials. We observed a striking dissociation: Whereas increased presentation frequency led to benefits in performance for both old and new test probes in CM search, it resulted in interference effects for both old and new test probes in VM search. Formal modeling suggested that a form of item-response learning took place in both conditions: Each presentation of a test probe led to the storage of that test probe-along with its associated "old" or "new" response-as an exemplar in LTM. These item-response pairs were retrieved along with current-list items in driving observers' old-- recognition judgments. We conclude that item-response learning is a core component of the LTM mechanisms that influence CM and VM memory search.

Beta-band activity represents the recent past during episodic encoding.

While much research has focused on understanding how individual stimuli are encoded in episodic memory, less is known about how a series of events is bound into a coherent episode. Cognitive models of episodic memory propose that information about presented stimuli is integrated into a composite representation reflecting one's past experience, allowing events separated in time to become associated. Recent evidence suggests that neural oscillatory activity may be critically involved in this process. To examine how oscillatory activity contributes to binding of information across events, we measured scalp EEG as participants studied categorized lists of people, places, and objects. We assessed their memory for the lists using free recall, allowing us to characterize the temporal and semantic organization of the studied items in memory. Using pattern classification, we identified EEG activity during encoding at a range of frequencies and scalp locations that was sensitive to the category of presented stimuli. In the beta band (16-25Hz) at right posterior electrodes, we observed activity that was also sensitive to the category of recently presented stimuli. This neural activity showed two characteristics consistent with a representation of the recent past: It became stronger when multiple items from the same category were presented in succession, and it contained a fading trace of the previous category after a category shift. When items were separated by an inter-item distraction task, this integrative beta-band activity was disrupted. Distraction also led to decreased semantic organization of the studied materials without affecting their temporal organization; this suggests that distraction disrupts the integration of semantic information over time, preventing encoding of items in terms of the semantic context of earlier items. Our results provide evidence that beta-band activity is involved in maintaining information about recent events, allowing construction of a coherent representation of a temporally extended episode in memory.

Response-time evidence for mixed memory states in a sequential-presentation change-detection task.

Response-time (RT) and choice-probability data were obtained in a rapid visual sequential-presentation change-detection task in which memory set size, study-test lag, and objective change probabilities were manipulated. False "change" judgments increased dramatically with increasing lag, consistent with the idea that study items with long lags were ejected from a discrete-slots buffer. Error RTs were nearly invariant with set size and lag, consistent with the idea that the errors were produced by a stimulus-independent guessing process. The patterns of error and RT data could not be explained in terms of encoding limitations, but were consistent with the hypothesis that long retention lags produced a zero-stimulus-information state that required guessing. Formal modeling of the change-detection RT and error data pointed toward a hybrid model of visual working memory. The hybrid model assumed mixed states involving a combination of memory and guessing, but with higher memory resolution for items with shorter retention lags. The work raises new questions concerning the nature of the memory representations that are produced across the closely related tasks of change detection and visual memory search.

Familiarity and categorization processes in memory search.

A fundamental distinction in tasks of memory search is whether items receive varied mappings (targets and distractors switch roles across trials) or consistent mappings (targets and distractors never switch roles). The type of mapping often produces markedly different performance patterns, but formal memory-based models that account quantitatively for detailed aspects of the results have not yet been developed and evaluated. Experiments were conducted to test a modern exemplar-retrieval model on its ability to account for memory-search performance involving a wide range of memory-set sizes in both varied-mapping (VM) and consistent-mapping (CM) probe-recognition tasks. The model formalized the idea that both familiarity-based and categorization-based processes operate. The model was required to fit detailed response-time (RT) distributions of individual, highly practiced subjects. A key manipulation involved the repetition of negative probes across trials. This manipulation produced a dramatic dissociation: False-alarm rates increased and correct-rejection RTs got longer in VM, but not in CM. The qualitative pattern of results and modeling analyses provided evidence for a strong form of categorization-based processing in CM, in which observers made use of the membership of negative probes in the "new" category to make old-new recognition decisions.

Investigating the effects of context, visual working memory, and inhibitory control in hybrid visual search.

Introduction: In real-life scenarios, individuals frequently engage in tasks that involve searching for one of the distinct items stored in memory. This combined process of visual search and memory search is known as hybrid search. To date, most hybrid search studies have been restricted to average observers looking for previously well-memorized targets in blank backgrounds. Methods: We investigated the effects of context and the role of memory in hybrid search by modifying the task's memorization phase to occur in all-new single trials. In addition, we aimed to assess how individual differences in visual working memory capacity and inhibitory control influence performance during hybrid search. In an online experiment, 110 participants searched for potential targets in images with and without context. A change detection and go/no-go task were also performed to measure working memory capacity and inhibitory control, respectively. Results: We show that, in target present trials, the main hallmarks of hybrid search remain present, with a linear relationship between reaction time and visual set size and a logarithmic relationship between reaction time and memory set size. These behavioral results can be reproduced by using a simple drift-diffusion model. Finally, working memory capacity did not predict most search performance measures. Inhibitory control, when relationships were significant, could account for only a small portion of the variability in the data. Discussion: This study provides insights into the effects of context and individual differences on search efficiency and termination.

Timing of internal processes: Investigating introspection about the costs of task switching and memory search.

During the last two decades, there has been new interest in introspection about multitasking performance. In this field, subjective timing of one's own reaction times (introspective RTs) has proven a useful measure to assess introspection. However, whether timing our own cognitive processing makes use of the same timing mechanisms as timing external intervals has been called into question. Here we take a novel approach to this question and build on the previously observed dissociation between the interference of task switching and memory search with a concurrent time production task whereby temporal productions increased with increasing memory set size but were not affected by switch costs. We tested whether a similar dissociation could be observed in this paradigm when participants provide introspective RTs instead of concurrent temporal productions. The results showed no such dissociation as switch costs and the effect of memory set size on RTs were both reflected in introspective RTs. These findings indicate that the underlying timing mechanisms differ between temporal productions and introspective RTs in this multitasking context, and that introspective RTs are still strikingly accurate estimates of objective RTs.

A guide to area-restricted search: a foundational foraging behaviour.

Area-restricted search is the capacity to change search effort adaptively in response to resource encounters or expectations, from directional exploration (global, extensive search) to focused exploitation (local, intensive search). This search pattern is used by numerous organisms, from worms and insects to humans, to find various targets, such as food, mates, nests, and other resources. Area-restricted search has been studied for at least 80 years by ecologists, and more recently in the neurological and psychological literature. In general, the conditions promoting this search pattern are: (1) clustered resources; (2) active search (e.g. not a sit-and-wait predator); (3) searcher memory for recent target encounters or expectations; and (4) searcher ignorance about the exact location of targets. Because area-restricted search adapts to resource encounters, the search can be performed at multiple spatial scales. Models and experiments have demonstrated that area-restricted search is superior to alternative search patterns that do not involve a memory of the exact location of the target, such as correlated random walks or Lévy walks/flights. Area-restricted search is triggered by sensory cues whereas concentrated search in the absence of sensory cues is associated with other forms of foraging. Some neural underpinnings of area-restricted search are probably shared across metazoans, suggesting a shared ancestry and a shared solution to a common ecological problem of finding clustered resources. Area-restricted search is also apparent in other domains, such as memory and visual search in humans, which may indicate an exaptation from spatial search to other forms of search. Here, we review these various aspects of area-restricted search, as well as how to identify it, and point to open questions.

Semantic Memory Search and Retrieval in a Novel Cooperative Word Game: A Comparison of Associative and Distributional Semantic Models.

Considerable work during the past two decades has focused on modeling the structure of semantic memory, although the performance of these models in complex and unconstrained semantic tasks remains relatively understudied. We introduce a two-player cooperative word game, Connector (based on the boardgame Codenames), and investigate whether similarity metrics derived from two large databases of human free association norms, the University of South Florida norms and the Small World of Words norms, and two distributional semantic models based on large language corpora (word2vec and GloVe) predict performance in this game. Participant dyads were presented with 20-item word boards with word pairs of varying relatedness. The speaker received a word pair from the board (e.g., exam-algebra) and generated a one-word semantic clue (e.g., math), which was used by the guesser to identify the word pair on the board across three attempts. Response times to generate the clue, as well as accuracy and latencies for the guessed word pair, were strongly predicted by the cosine similarity between word pairs and clues in random walk-based associative models, and to a lesser degree by the distributional models, suggesting that conceptual representations activated during free association were better able to capture search and retrieval processes in the game. Further, the speaker adjusted subsequent clues based on the first attempt by the guesser, who in turn benefited from the adjustment in clues, suggesting a cooperative influence in the game that was effectively captured by both associative and distributional models. These results indicate that both associative and distributional models can capture relatively unconstrained search processes in a cooperative game setting, and Connector is particularly suited to examine communication and semantic search processes.

Age doesn't matter much: hybrid visual and memory search is preserved in older adults.

We tested younger and older observers' attention and long-term memory functions in a "hybrid search" task, in which observers look through visual displays for instances of any of several types of targets held in memory. Apart from a general slowing, search efficiency did not change with age. In both age groups, reaction times increased linearly with the visual set size and logarithmically with the memory set size, with similar relative costs of increasing load (Experiment 1). We replicated the finding and further showed that performance remained comparable between age groups when familiarity cues were made irrelevant (Experiment 2) and target-context associations were to be retrieved (Experiment 3). Our findings are at variance with theories of cognitive aging that propose age-specific deficits in attention and memory. As hybrid search resembles many real-world searches, our results might be relevant to improve the ecological validity of assessing age-related cognitive decline.

Examining the effects of passive and active strategies on behavior during hybrid visual memory search: evidence from eye tracking.

Hybrid search requires observers to search both through a visual display and through the contents of memory in order to find designated target items. Because professional hybrid searchers such as airport baggage screeners are required to look for many items simultaneously, it is important to explore any potential strategies that may beneficially impact performance during these societally important tasks. The aim of the current study was to investigate the role that cognitive strategies play in facilitating hybrid search. We hypothesized that observers in a hybrid search task would naturally adopt a strategy in which they remained somewhat passive, allowing targets to "pop out." Alternatively, we considered the possibility that observers could adopt a strategy in which they more actively directed their attention around the visual display. In experiment 1, we compared behavioral responses during uninstructed, passive, and active hybrid search. We found that uninstructed search tended to be more active in nature, but that adopting a passive strategy led to above average performance as indicated by a combined measure of speed and accuracy called a balanced integration score (BIS). We replicated these findings in experiment 2. Additionally, we found that oculomotor behavior in passive hybrid search was characterized by longer saccades, improved attentional guidance, and an improved ability to identify items as targets or distractors (relative to active hybrid search). These results have implications for understanding hybrid visual search and the effect that strategy use has on performance and oculomotor behavior during this common, and at times societally important, task.

Use or Consequences: Probing the Cognitive Difference Between Two Measures of Divergent Thinking.

Recent studies have highlighted both similarities and differences between the cognitive processing that underpins memory retrieval and that which underpins creative thinking. To date, studies have focused more heavily on the Alternative Uses task, but fewer studies have investigated the processing underpinning other idea generation tasks. This study examines both Alternative Uses and Consequences idea generation with a methods pulled from cognitive psychology, and a novel method for evaluating the creativity of such responses. Participants were recruited from Amazon Mechanical Turk using a custom interface allowing for requisite experimental control. Results showed that both Alternative Uses and Consequences generation are well approximated by an exponential cumulative response time model, consistent with studies of memory retrieval. Participants were also slower to generate their first consequence compared with first responses to Alternative Uses, but inter-response time was negatively related to pairwise similarity on both tasks. Finally, the serial order effect is exhibited for both tasks, with Consequences earning more creative evaluations than Uses. The results have implications for burgeoning neuroscience research on creative thinking, and suggestions are made for future areas of inquiry. In addition, the experimental apparatus described provides an equitable way for researchers to obtain good quality cognitive data for divergent thinking tasks.

Semantic search during divergent thinking.

Divergent thinking, as a method of examining creative cognition, has not been adequately analyzed in the context of modern cognitive theories. This article casts divergent thinking responding in the context of theories of memory search. First, it was argued that divergent thinking tasks are similar to semantic fluency tasks, but are more constrained, and less well structured. Next, response time distributions from 54 participants were analyzed for temporal and semantic clustering. Participants responded to two prompts from the alternative uses test: uses for a brick and uses for a bottle, for two minutes each. Participants' cumulative response curves were negatively accelerating, in line with theories of search of associative memory. However, results of analyses of semantic and temporal clustering suggested that clustering is less evident in alternative uses responding compared to semantic fluency tasks. This suggests either that divergent thinking responding does not involve an exhaustive search through a clustered memory trace, but rather that the process is more exploratory, yielding fewer overall responses that tend to drift away from close associates of the divergent thinking prompt.

Aging Slows Access to Temporal Information From Working Memory.

OBJECTIVES: To evaluate the impact of aging on controlled memory search operations, we investigated the retrieval of temporal order information from working memory (WM). METHOD: Young and older adults completed a relative judgments-of-recency (JOR) task. In each trial, participants studied 5-item lists and were presented with two probes from the study list. Participants indicated the probe that had appeared more recently in the study list. RESULTS: Analyses of accuracy data showed that young adults were more successful in correctly detecting the more recent probe compared with older adults. To evaluate the retrieval dynamics, we applied Hacker's (1980) serial scanning model on reaction time data. Results from the model fits revealed that older adults were slower in engaging in the serial memory search operations required to access temporal order information from WM. DISCUSSION: These findings suggest that this age-related impairment in a JOR task might arise from a slower deployment of controlled memory operations, such as serial search.