Do item-dependent context representations underlie serial order in cognition? Commentary on Logan (2021)

Logan (2021) presented an impressive unification of serial order tasks including whole report, typing, and serial recall in the form of the context retrieval and updating (CRU) model. Despite the wide breadth of the model’s coverage, its reliance on encoding and retrieving context representations that consist of the previous items may prevent it from being able to address a number of critical benchmark findings in the serial order literature that have shaped and constrained existing theories. In this commentary, we highlight three major challenges that motivated the development of a rival class of models of serial order, namely positional models. These challenges include the mixed-list phonological similarity effect, the protrusion effect, and interposition errors in temporal grouping. Simulations indicated that CRU can address the mixed list phonological similarity effect if phonological confusions can occur during its output stage, suggesting that the serial position curves from this paradigm do not rule out models that rely on inter-item associations, as has been previously been suggested. The other two challenges are more consequential for the model’s representations, and simulations indicated the model was not able to provide a complete account of them. We highlight and discuss how revisions to CRU’s representations or retrieval mechanisms can address these phenomena and emphasize that a fruitful direction forward would be to either incorporate positional representations or approximate them with its existing representations.

EXPRESS: Temporal grouping effects in verbal and musical short-term memory: Is serial order representation domain-general?

The question of the domain-general versus domain-specific nature of the serial order mechanisms involved in short-term memory is currently under debate. The present study aimed at addressing this question through the study of temporal grouping effects in short-term memory tasks with musical material, a domain which has received little interest so far. The goal was to determine whether positional coding—currently the best account of grouping effect in verbal short-term memory—represents a viable mechanism to explain grouping effects in the musical domain. In a first experiment, non-musicians performed serial reconstruction of 6-tone sequences, where half of the sequences was grouped by groups of three items and the other half presented at a regular pace. The overall data pattern suggests that temporal grouping exerts on tone sequences reconstruction the same effects as in the verbal domain, except for ordering errors which were not characterized by the typical increase of interpositions. This pattern has been replicated in two additional experiments with verbal material, using the same grouping structure as in the musical experiment. The findings support that verbal and musical short-term memory domains are characterized by similar temporal grouping effects for the recall of 6-item lists grouped by three, but it also suggests the existence of boundary condition to observe an increase of interposition errors predicted by positional theories.

Temporal binding window and sense of agency are related processes modifiable via occipital tACS

The temporal binding window refers to the time frame within which temporal grouping of sensory information takes place. Sense of agency is the feeling of being in control of one’s actions, and their associated outcomes. While previous research has shown that temporal cues and multisensory integration play a role in sense of agency, no studies have directly assessed whether individual differences in the temporal binding window and sense of agency are associated. In all three experiments, to assess sense of agency, participants pressed a button triggering, after a varying delay, the appearance of the circle, and reported their sense of agency over the effect. To assess the temporal binding window a simultaneity judgment task (Experiment 1) and a double-flash illusion task (Experiment 2 and 3) was also performed. As expected, the temporal binding window correlated with the sense of agency window. In Experiment 3, these processes were modulated by applying occipital tACS at either 14Hz or 8Hz. We found 14Hz tACS stimulation was associated with narrower temporal biding window and sense of agency window. Our results suggest the temporal binding window and the time window of sense of agency are related. They also point towards a possible underlying neural mechanism (alpha peak frequency) for this association.

EXPRESS: Grouping Effects in Immediate Reconstruction of Order and the Preconditions for Long-term Learning

One commonly acknowledged role of working memory is to set up conditions for new learning. Yet, it has long been understood that there is not a perfect correspondence between conditions leading to good immediate recall from working memory and conditions leading to good delayed recall from long-term memory. Here, in six experiments, we investigated the relation between grouping effects in immediate and delayed reconstruction of order for word lists. There has been a striking absence of tests of grouping effects in long-term memory. In the first four experiments, items within groups are presented concurrently, which encourages associations between items in a group. Despite that presumably favorable situation for group learning, in Experiments 1 and 2 we found effects of grouping only in immediate order reconstruction and not in delayed reconstruction. When more processing time was allowed (Experiments 3 & 4), grouping effects in both immediate and delayed order reconstruction were obtained. Experiment 5 showed that, with items presented one at a time, but with roughly the same amount of processing time and spatial separation as the previous two experiments, grouping effects were obtained neither in immediate order reconstruction nor in delayed reconstruction. However, in Experiment 6 with a more salient manipulation of grouping, effects of grouping were obtained in immediate order reconstruction, but not in delayed reconstruction. In sum, we demonstrated for the first time that there are mechanisms of temporal grouping that assist working memory but are relatively ineffective for long-term learning, in contrast to more effective, concurrent presentation.

Spontaneous grouping of saccade timing in the presence of task-irrelevant objects

Sequential movements are often grouped into several chunks, as evidenced by the modulation of the timing of each elemental movement. Even during synchronized tapping with a metronome, we sometimes feel subjective accent for every few taps. To examine whether motor segmentation emerges during synchronized movements, we trained monkeys to generate a series of predictive saccades synchronized with visual stimuli which sequentially appeared for a fixed interval (400 or 600 ms) at six circularly arranged landmark locations. We found two types of motor segmentations that featured periodic modulation of saccade timing. First, the intersaccadic interval (ISI) depended on the target location and saccade direction, indicating that particular combinations of saccades were integrated into motor chunks. Second, when a task-irrelevant rectangular contour surrounding three landmarks ("inducer") was presented, the ISI significantly modulated depending on the relative target location to the inducer. All patterns of individual differences seen in monkeys were also observed in humans. Importantly, the effects of the inducer greatly decreased or disappeared when the animals were trained to generate only reactive saccades (latency >100 ms), indicating that the motor segmentation may depend on the internal rhythms. Thus, our results demonstrate two types of motor segmentation during synchronized movements: one is related to the hierarchical organization of sequential movements and the other is related to the spontaneous grouping of rhythmic events. This experimental paradigm can be used to investigate the underlying neural mechanism of temporal grouping during rhythm production.

Semantic Knowledge Constrains the Processing of Serial Order Information in Working Memory

Long-term memory knowledge is considered to impact short-term maintenance of item information in working memory, as opposed to short-term maintenance of serial order information. Evidence supporting an impact of semantic knowledge on serial order maintenance remains weak. In the present study, we demonstrate that semantic knowledge can impact the processing of serial order information in a robust manner. Experiment 1 manipulated semantic relatedness effect by using semantic categories presented in subgroups of items (leaf – tree – branch – cloud – sky – rain). This semantic grouping manipulation was compared to a temporal grouping manipulation whose impact on the processing of serial order information is well-established. Both the semantic and temporal grouping manipulations constrained the occurrence of serial order errors in a robust manner: when migrating to a non-target serial position, items tended to do so most of the time toward the position of a semantically related item or within the same temporal group. Critically, this impact of semantic knowledge on the pattern of migration errors was not observed anymore in Experiment 2, in which we broke-up the semantic groups, by presenting the semantically related items an interleaved fashion (leaf – cloud – tree – sky – branch – rain). Both semantic and temporal grouping factors may reflect a general mechanism through which information is represented hierarchically. Alternatively, both factors could result from the syntactic and/or semantic regularities that naturally structure linguistic information. These results support models considering direct interactions between serial order and linguistic components of WM.

Temporal grouping effects in tone sequence reconstruction: testing domain-general positional theories of serial order

The question of the domain-general versus domain-specific nature of the serial order mechanisms involved in short-term memory is currently under debate. The present study aimed at addressing this question through the study of temporal grouping effects in short-term memory tasks with musical material, a domain which has received little interest so far. We conducted three experiments with non-musicians who performed serial reconstruction of six-tone sequences, where half of the sequences were temporally grouped and the other half presented at a regular pace. The overall data pattern suggests that temporal grouping exerts the same effects on tone sequences reconstruction as in the verbal domain, except for ordering errors. This pattern was replicated in a fourth experiment with verbal material of the same structure as in musical memory experiments of this study. Our findings support the view that positional markers similar to those described in the verbal domain of short-term memory could be used to represent serial order in the musical domain of short-term memory.

The influence of rhythm on short-term memory for serial order

In the field of verbal short-term memory (STM), numerous theoretical models have been proposed to explain how serial order information is processed and represented. Evidence suggests that serial order is represented through associations between items and a varying contextual signal coding the position of each item in a sequence, but the nature of this contextual signal is still a matter of debate (i.e., event-based vs. time-based varying signal). According to event-based models of serial order, the contextual signal coding serial order is not sensitive to temporal manipulations, as it is the case in irregularly timed sequences. Up to now, the study of the temporal factors influencing serial order STM has been limited to temporal grouping and temporal isolation effects. The goal of the present study is to specify in more detail the role played by temporal factors in serial order STM tasks. To accomplish this, we compared recall performance and error patterns for sequences presenting items at a regular or an irregular and unpredictable timing in three experiments. The results showed that irregular timing does not affect serial recall nor the pattern of errors. These data clearly favour the view that serial order in verbal STM is represented with event-based rather than time-based codes.