Breaking the cardinal rule: The impact of interitem interaction and attentional priority on the cardinal biases in orientation working memory

Enhanced Working Memory Representations for Rare Events

Rare events ( oddballs ) produce a variety of enhanced physiological responses relative to frequent events ( standards ), including the P3b component of the event-related potential (ERP) waveform. Previous research has suggested that the P3b is related to working memory, which implies that working memory representations will be enhanced for rare stimuli. To test this hypothesis, we devised a modified oddball paradigm where a target disk was presented at one of 16 different locations, which were divided into rare and frequent sets. Participants made a binary response on each trial to report whether the target appeared in the rare set or the frequent set. As expected, the P3b was much larger for stimuli appearing at a location within the rare set. We also included occasional probe trials in which the subject reported the exact location of the target. Accuracy was higher for rare than frequent locations. In addition, memory reports on rare trials were more accurate in participants with larger P3b amplitudes on rare trials (although reports were not more accurate for trials with larger P3b amplitudes within participants). We also applied multivariate pattern analysis to the ERP data to "decode" the remembered location of the target. Decoding accuracy was greater for locations within the rare set than for locations within the frequent set. We then replicated and extended our behavioral findings in a follow-up experiment. These behavioral and electrophysiological results demonstrate that although both frequent and rare events are stored in working memory, working memory performance is enhanced for rare oddball events.

Impact Statement

For many decades, researchers have observed that rare events elicit a broad range of physiological responses, and there has been much speculation about the functional significance of these responses. One such response is the P3b component, which is a large voltage deflection in scalp EEG recordings. Over 40 years ago, the P3b was hypothesized to reflect "context updating" (now often called "working memory updating"). However, there has been no direct evidence that working memory is actually enhanced for rare, P3b-eliciting events. In the present study, we found that both behavioral and electrophysiological measures of working memory were enhanced for rare events. However, it is not clear that the increased P3b-related brain activity actually caused the enhancement of working memory.

Impact of conflicts between long- and short-term priors on the weighted prior integration in visual perception

The prior distribution of values for a specific feature can be categorized as long- or short-term priors based on their respective learning durations. Studies have demonstrated that the visual system can integrate both priors through weighted averaging and then utilize the integrated prior to efficiently encode stimuli. It is unclear what determines the two priors' relative weights. To address this question, we arranged the orientations according to three distributions: natural, anti-natural, and natural with increased-amplitude distributions. The natural distribution mirrors the distribution of orientations in the natural world, so it does not conflict with the long-term prior; according to the Kullback-Leibler divergence analysis, the natural distribution had a higher conflict with the anti-natural distribution than with the natural distribution with increased amplitude. It was found that the cardinal bias - the orientation estimates are biased away from the cardinal orientations - was strongest in the natural distribution with increased amplitude but weakest in the anti-natural distribution. These results were accurately predicted by an efficient Bayesian observer model in which the prior is the weighted integration of the long- and short-term priors. Importantly, the weight of the short-term prior in the new prior decreased as the level of the conflict between the long- and short-term priors increased. Therefore, this study reveals that the visual system integrates the long- and short-term priors through weighted averaging, with the conflicting level between the two priors determining their relative weights in the integration prior. The integrated prior was used by visual systems to efficiently encode stimuli.

Color category and inter-item interaction influence color working memory codependently

Our brains do not always encode visual information in a veridical way. Visual working memory (WM) for features such as color can be biased. WM bias comes from several sources. Category priors can lead to WM bias. For example, color WM is biased toward or away from category prototypes. In addition to category knowledge, contextual factors can induce and modulate WM bias; however, these biases of different sources have usually been investigated independently with different tasks. The present study sought to explore how color WM is influenced by both color category and concurrent distractor. Specifically, we asked participants to retain two color items in WM to investigate how the WM representation of the target color is biased by learned category knowledge and contextual inter-item interactions. Our study found that the WM representation of the target color is biased toward or away from the category prototypes and away from the distractor color that is simultaneously held in WM, indicating that both color category and concurrent distractor bias color WM. More importantly, the weight of these two biases depends on the specific color category, suggesting that category priors and inter-item interaction biases are not simply additive but flexible. Furthermore, we revealed that both types of biases arise from perceptual processes.

Repulsion bias is insensitive to spatial attention, yet expands during active working memory maintenance

Our brain sometimes represents visual information in a biased manner. Multiple visual features presented simultaneously or sequentially may interact with each other when we perceive them or maintain them in visual working memory (WM), giving rise to report bias. How goal-directed attention influences target representation is not fully understood, especially concerning whether attention towards distractors modulates report bias for the target. Our study investigated the WM biases of the target when it is concurrent with (1) one attended distractor only, (2) one unattended distractor only, and (3) both kinds of distractors during perception. It was found that the target WM is reported as being repelled away from concurrent distractors, attended or unattended, suggesting attention is not necessary for the occurrence of repulsion bias during perception. Furthermore, goal-directed attention towards the distractors modulates the strength of interitem interaction, and the repulsion bias was found to be stronger when attention was directed toward the distractor than when it was not. However, the exaggerated repulsion associated with the attended distractor is likely due to increased relevance to the memory task and (or) WM load instead of spatial attention. In contrast, spatial attention towards the distractor increases the chances of misreporting the distractor for the target.

Cardinal bias interacts with the stimulus history bias in orientation working memory

Reports in a visual working memory(WM) task exhibit biases related to the categorical structure of the stimulus space (e.g., cardinal bias) as well as biases related to previously seen stumuli (e.g., serial bias). While these biases are common and can occur simultaneously, the extent to which they interact in WM remains unknown. In the present study, I used orientation delayed estimation tasks known to produce both cardinal and serial biases and found that the serial bias systematically varied based on the relative positions of the cardinal axis and the preceding stimulus in orientation space. When they were positioned in a way that generated cardinal and serial biases in the same direction (i.e., on the same side of the target orientation), reports for the target orientation exhibited a regular repulsive serial bias. However, when their positions resulted in the biases in the opposite directions (i.e., on the opposite side of the target orientation), no serial bias occurred. This absence of serial bias was replicated in a follow-up experiment where the locations of the stimulus orientation and the response probe were completely randomized, suggesting that the interaction occurs independently from location-based response preparation processes. Together, these results demonstrate that the prior stimulus and the cardinal axis impose interactive impact on the processing of new stimulus, producing differential patterns of serial bias depending on the specific stimulus being processed. These findings place significant implications on computational models addressing the nature of the stimulus history effect and its underlying mechanisms.