Reactivating ordinal position information from auditory sequence memory in human brains

Maintenance of color memoranda in activity-quiescent working memory states: Evidence from impulse perturbation

In the present study, we used an impulse perturbation method to probe working memory maintenance of colors in neurally active and activity-quiescent states, focusing on a set of pre-registered analyses. We analyzed the electroencephalograph (EEG) data of 30 participants who completed a delayed match-to-sample working memory task, in which one of the two items that were presented was retro-cued as task relevant. The analyses revealed that both cued and uncued colors were decodable from impulse-evoked activity, the latter in contrast to previous reports of working memory for orientation gratings. Decoding of colors from oscillations in the alpha band showed that cued items could be decoded therein whereas uncued items could not. Overall, the outcomes suggest that subtle differences exist between the representation of colors, and that of stimuli with spatial properties, but the present results also demonstrate that regardless of their specific neural state, both are accessible through visual impulse perturbation.

Electrophysiological hallmarks for event relations and event roles in working memory

The ability to maintain events (i.e., interactions between/among objects) in working memory is crucial for our everyday cognition, yet the format of this representation is poorly understood. The current ERP study was designed to answer two questions: How is maintaining events (e.g., the tiger hit the lion) neurally different from maintaining item coordinations (e.g., the tiger and the lion)? That is, how is the event relation (present in events but not coordinations) represented? And how is the agent, or initiator of the event encoded differently from the patient, or receiver of the event during maintenance? We used a novel picture-sentence match-across-delay approach in which the working memory representation was "pinged" during the delay, replicated across two ERP experiments with Chinese and English materials. We found that maintenance of events elicited a long-lasting late sustained difference in posterior-occipital electrodes relative to non-events. This effect resembled the negative slow wave reported in previous studies of working memory, suggesting that the maintenance of events in working memory may impose a higher cost compared to coordinations. Although we did not observe significant ERP differences associated with pinging the agent vs. the patient during the delay, we did find that the ping appeared to dampen the ongoing sustained difference, suggesting a shift from sustained activity to activity silent mechanisms. These results suggest a new method by which ERPs can be used to elucidate the format of neural representation for events in working memory.

Impulse perturbation reveals cross-modal access to sensory working memory through learned associations

We investigated if learned associations between visual and auditory stimuli can afford full cross-modal access to working memory. Previous research using the impulse perturbation technique has shown that cross-modal access to working memory is one-sided; visual impulses reveal both auditory and visual memoranda, but auditory impulses do not seem to reveal visual memoranda (Wolff et al., 2020b). Our participants first learned to associate six auditory pure tones with six visual orientation gratings. Next, a delayed match-to-sample task for the orientations was completed, while EEG was recorded. Orientation memories were recalled either via their learned auditory counterpart, or were visually presented. We then decoded the orientation memories from the EEG responses to both auditory and visual impulses presented during the memory delay. Working memory content could always be decoded from visual impulses. Importantly, through recall of the learned associations, the auditory impulse also evoked a decodable response from the visual WM network, providing evidence for full cross-modal access. We also observed that after a brief initial dynamic period, the representational codes of the memory items generalized across time, as well as between perceptual maintenance and long-term recall conditions. Our results thus demonstrate that accessing learned associations in long-term memory provides a cross-modal pathway to working memory that seems to be based on a common coding scheme.