The ordinal distance effect in working memory: does it exist in the absence of confounds?

In most daily-life situations, briefly remembering actions or words is not sufficient to reach a goal. You often have to remember them in a specific order. One behavioural observation of the processing of ordinal information in working memory is the ordinal distance effect. It refers to the facilitation in the ordinal processing of items that are at distant positions in comparison to items close to each other in working memory. So far, the ordinal distance effect has always been investigated with a simultaneous presentation of the items of the memory sequences. Such a presentation created a confound: items distant by their ordinal distance were also distant by their physical distance (i.e., the visuospatial distance between their positions on the screen). In the present study, we investigated whether the ordinal distance effect can be observed in the absence of a physical confound using a sequential presentation of the items of the memory sequence. Our findings revealed a combination of reversed and standard distance effects, unchanged by physical characteristics. The presence of a reversed distance effect suggests that a serial scanning strategy confers an advantage for adjacent items. Different strategies apply to the ordinal judgment of adjacent versus more distant items in verbal working memory. Interestingly, when ruling out the confound of primacy and recency effects, the standard distance effect disappeared while the reversed distance effect remained. Ultimately, our findings question the existence of the ordinal distance effect as a separate effect from other working memory confounds.

Hemispatial neglect and serial order in verbal working memory.

Working memory refers to our ability to actively maintain and process a limited amount of information during a brief period of time. Often, not only the information itself but also its serial order is crucial for good task performance. It was recently proposed that serial order is grounded in spatial cognition. Here, we compared performance of a group of right hemisphere-damaged patients with hemispatial neglect to healthy controls in verbal working memory tasks. Participants memorized sequences of consonants at span level and had to judge whether a target consonant belonged to the memorized sequence (item task) or whether a pair of consonants were presented in the same order as in the memorized sequence (order task). In line with this idea that serial order is grounded in spatial cognition, we found that neglect patients made significantly more errors in the order task than in the item task compared to healthy controls. Furthermore, this deficit seemed functionally related to neglect severity and was more frequently observed following right posterior brain damage. Interestingly, this specific impairment for serial order in verbal working memory was not lateralized. We advance the hypotheses of a potential contribution to the deficit of serial order in neglect patients of either or both (1) reduced spatial working memory capacity that enables to keep track of the spatial codes that provide memorized items with a positional context, (2) a spatial compression of these codes in the intact representational space.

Continuous track paths reveal additive evidence integration in multistep decision making.

Multistep decision making pervades daily life, but its underlying mechanisms remain obscure. We distinguish four prominent models of multistep decision making, namely serial stage, hierarchical evidence integration, hierarchical leaky competing accumulation (HLCA), and probabilistic evidence integration (PEI). To empirically disentangle these models, we design a two-step reward-based decision paradigm and implement it in a reaching task experiment. In a first step, participants choose between two potential upcoming choices, each associated with two rewards. In a second step, participants choose between the two rewards selected in the first step. Strikingly, as predicted by the HLCA and PEI models, the first-step decision dynamics were initially biased toward the choice representing the highest sum/mean before being redirected toward the choice representing the maximal reward (i.e., initial dip). Only HLCA and PEI predicted this initial dip, suggesting that first-step decision dynamics depend on additive integration of competing second-step choices. Our data suggest that potential future outcomes are progressively unraveled during multistep decision making.