Brian McElree

Working Memory and Focal Attention

Measures of retrieval speed indicated that only a small subset of representations in working memory falls within the focus of attention. An n-back task, which required tracking an item 1, 2, or 3 back in a sequentially presented list, was used to examine the representation and retrieval of recent events and how control processes can be used to maintain an item in focal attention while concurrently processing new information. A speed-accuracy trade-off procedure was used to derive measures of the availability and the speed with which recent events can be accessed. Results converge with other time course studies in demonstrating that attention can be concurrently allocated only to a small number of memory representations, perhaps just 1 item. Measures of retrieval speed further demonstrate that order information is retrieved by a slow search process when an item is not maintained within focal attention.

Covert attention accelerates the rate of visual information processing

Whenever we open our eyes, we are confronted with an overwhelming amount of visual information. Covert attention allows us to select visual information at a cued location, without eye movements, and to grant such information priority in processing. Covert attention can be voluntarily allocated, to a given location according to goals, or involuntarily allocated, in a reflexive manner, to a cue that appears suddenly in the visual field. Covert attention improves discriminability in a wide variety of visual tasks. An important unresolved issue is whether covert attention can also speed the rate at which information is processed. To address this issue, it is necessary to obtain conjoint measures of the effects of covert attention on discriminability and rate of information processing. We used the response-signal speed-accuracy tradeoff (SAT) procedure to derive measures of how cueing a target location affects speed and accuracy in a visual search task. Here, we show that covert attention not only improves discriminability but also accelerates the rate of information processing.

Memory structures that subserve sentence comprehension

Measures of the speed and accuracy of processing sentences with nonadjacent dependencies derived from the response-signal speed-accuracy tradeoff procedure were used to examine the nature of the memory system that underlies sentence comprehension. Three experiments with different sentence structures demonstrated that the accuracy of processing a dependency decreased as more material was interpolated between nonadjacent constituents. However, processing speed was unaffected by the amount of interpolated material, indicating that memory representations for previously processed constituents can be accessed directly. These results suggest that a content-addressable memory system mediates sentence comprehension, in which syntactic and semantic information provide direct access to memory representations without the need to search through extraneous representations. Notably, content-addressability appears to underlie the interpretation of sentence structures that also require the recovery of order information, a type of operation that has been shown to necessitate a slow search process in list-learning experiments (McElree, 2001; McElree & Dosher, 1993).

Accessing Recent Events

Publisher Summary This chapter reviews the speed and accuracy of accessing representations of recently processed information. It documents the types of retrieval operations used to access both item and order information. Evidence is presented indicating that item information is retrieved with a direct-access (content-addressable) process whereas order information is retrieved by a slower serial search process. The chapter emphasizes on focal attention. Information in focal attention can be discriminated from information in a more passive state by its relatively fast retrieval dynamics. This view is reinforced by two new experiments that measure changes in retrieval dynamics that result from explicit attempts to shunt information from memory to focal attention. Estimates of focal attention based on retrieval speed measures indicate that it has a much smaller capacity than has typically been assumed in some current approaches. This view is reinforced further by studies that challenge subjects to attempt to retain items in focal attention while concurrently processing other information. The chapter consludes with a discussion of neuroimaging findings.

The temporal dynamics of visual search: Evidence for parallel processing in feature and conjunction searches

Feature and conjunction searches have been argued to delineate parallel and serial operations in visual processing. The authors evaluated this claim by examining the temporal dynamics of the detection of features and conjunctions. The 1st experiment used a reaction time (RT) task to replicate standard mean RT patterns and to examine the shapes of the RT distributions. The 2nd experiment used the response-signal speed-accuracy trade-off (SAT) procedure to measure discrimination (asymptotic detection accuracy) and detection speed (processing dynamics). Set size affected discrimination in both feature and conjunction searches but affected detection speed only in the latter. Fits of models to the SAT data that included a serial component overpredicted the magnitude of the observed dynamics differences. The authors concluded that both features and conjunctions are detected in parallel. Implications for the role of attention in visual processing are discussed.

Isolating the contributions of familiarity and source information to item recognition: a time course analysis.

Recognition memory may be mediated by the retrieval of distinct types of information, notably, a general assessment of familiarity and the recovery of specific source information. A response-signal speed-accuracy trade-off variant of an exclusion procedure was used to isolate the retrieval time course for familiarity and source information. In 2 experiments, participants studied spoken and read lists (with various numbers of presentations) and then performed an exclusion task, judging an item as old only if it was in the heard list. Dual-process fits of the time course data indicated that familiarity information typically is retrieved before source information. The implications that these data have for models of recognition, including dual-process and global memory models, are discussed.

Serial retrieval processes in the recovery of order information

The retrieval of temporal order and item information from short-term memory (STM) are examined with the cued-response speed-accuracy trade-off (CR-SAT) procedure and a complementary reaction time (RT) task. The retrieval of order information was examined with a two-alternative forced-choice (2AFC), relative judgment of recency (JOR) task. Analyses of the pattern of mean RT, RT accuracy, and the overall shape of the RT distribution for correct JORs suggest that order information is retrieved by a serial retrieval mechanism. Analyses of SAT retrieval functions confirm that order information is retrieved by a recency-based, serial retrieval process. These results contrast with previous SAT analyses of STM item recognition (B. McElree & B. A. Dosher, 1989), which indicate that item information is retrieved by a parallel or direct-access mechanism. The dissociation between item and order information retrieval was further documented in a 2AFC item recognition SAT study

Sentence comprehension is mediated by content-addressable memory structures.

Studies of working memory demonstrate that some forms of information are retrieved by a content-addressable mechanism (McElree & Dosher, 1989; McElree, 1996, 1998), whereas others require a slower search-based mechanism (McElree & Dosher, 1993). Measures of the speed and accuracy of processing sentences with filler-gap dependencies demonstrate that the probability of maintaining a representation of a filler item decreases as additional material is processed, but that the speed with which a preserved representation is accessed is unaffected by the amount of interpolated material. These results suggest that basic binding operations in sentence comprehension are mediated by a content-addressable memory system.

Working memory retrieval: Contributions of the left prefrontal cortex, the left posterior parietal cortex, and the hippocampus

Functional magnetic resonance imaging was used to identify regions involved in working memory (WM) retrieval. Neural activation was examined in two WM tasks: an item recognition task, which can be mediated by a direct-access retrieval process, and a judgment of recency task that requires a serial search. Dissociations were found in the activation patterns in the hippocampus and in the left inferior frontal gyrus (LIFG) when the probe contained the most recently studied serial position (where a test probe can be matched to the contents of focal attention) compared to when it contained all other positions (where retrieval is required). The data implicate the hippocampus and the LIFG in retrieval from WM, complementing their established role in long-term memory. Results further suggest that the left posterior parietal cortex (LPPC) supports serial retrieval processes that are often required to recover temporal order information. Together, these data suggest that the LPPC, the LIFG, and the hippocampus collectively support WM retrieval. Critically, the reported findings support accounts that posit a distinction between representations maintained in and outside of focal attention, but are at odds with traditional dual-store models that assume distinct mechanisms for short- and long-term memory representations.

Coercion in sentence processing: evidence from eye-movements and self-paced reading

Seemingly simple expressions may require an enriched form of interpretative processing. Verbs like began and finished can be used felicitously only when one of their arguments denotes an event (e.g., reading). However, such verbs commonly appear with noun phrases whose literal interpretations denote entities (e.g., the book). It has been suggested that readers and listeners have to undertake additional computations to interpret strings like began the book that are not required when the book is interpreted as an entity (e.g., Pustejovsky, 1995). If so, began the book should be harder to process than strings like read the book, when the verb does not require an argument that denotes an event, or strings like began the fight, when the argument denotes an event. Experiment 1 found evidence from eye movements showing that entity noun phrases take longer to process following verbs that require event arguments than verbs that do not. Experiments 2 and 3, using eye-tracking and self-paced reading, respectively, found that difficulty did not appear when verbs like began had arguments that referred to events. We interpret the results with respect to accounts of semantic processing.