Author response: Jointly looking to the past and the future in visual working memory

Liu, Baiwei; Alexopoulou, Zampeta-Sofia; van Ede, Freek · 2024 · Crossref

DOI: 10.7554/elife.90874.2.sa3

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Summary

This study investigates how visual working memory integrates past sensory information with future behavioral demands. While working memory inherently bridges past inputs and future actions, conventional laboratory tasks often conflate these components by encoding and testing stimuli at the same spatial location. The authors address the underexplored question of whether the brain codes internal representations with regard to past, future, or both locations when these attributes are dissociated. To answer this, they developed a task that experimentally isolated past (encoded) and future (to-be-tested) memory attributes, tracking their utilization through gaze behavior in healthy human volunteers. The experimental design involved 25 participants performing a visual working memory task where two colored gratings were encoded at either vertical or horizontal positions. Crucially, the test phase always occurred on the orthogonal axis, dissociating the encoding location from the testing location. A "future rule," stable within each session, determined which test stimulus was relevant based on the encoded item’s position. After a delay, a color cue prompted participants to select the relevant memory item. The researchers analyzed spatial biases in saccades, specifically microsaccades, following the cue to determine if gaze shifted toward the past encoded location, the future test location, or both. The results revealed that participants jointly considered both past and future locations during mnemonic selection. Gaze biases toward the encoded (past) location emerged approximately 200 ms after the cue, indicating that retention relies on past locations even when they are not directly tested. Simultaneously, significant biases toward the future (to-be-tested) location emerged in overlapping time windows. Single-trial analysis of individual saccades demonstrated a dependency between these biases: saccades biased toward the past were also biased toward the future, and vice versa. This interaction confirms that past and future attributes are not processed independently or serially but are truly jointly activated at the single-saccade level. These findings challenge the notion that memory representations are remapped solely to future-relevant locations or that past attributes are discarded once irrelevant. Instead, the study demonstrates that working memory simultaneously retains and accesses both past and future spatial attributes. This joint consideration suggests that maintaining multiple spatial frames may enhance the robustness and flexibility of memory representations, allowing them to serve dynamic, evolving behavioral demands. The work provides key support for the view that memory is fundamentally future-oriented while retaining past information, offering new insights into the interplay between vision, eye movements, and memory.

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• working memory