Role of time in binding features in visual working memory

Previous research on feature binding in visual working memory has supported a privileged role for location in binding an object's non-spatial features. However, humans are able to correctly recall feature conjunctions of objects that occupy the same location at different times. In a series of behavioral experiments, we investigated binding errors under these conditions, and specifically tested whether ordinal position can take the role of location in mediating feature binding. We performed two dual-report experiments in which participants had to memorize three colored shapes presented sequentially at the screen center. When participants were cued with the ordinal position of one item and had to report its shape and color, report errors for the two features were largely uncorrelated. In contrast, when participants were cued e.g. with an item's shape and reported an incorrect ordinal position, they had a high chance of making a corresponding error in the color report. This pattern of error correlations closely matched the predictions of a model in which color and shape are bound to each other only indirectly via an item's ordinal position. In a third experiment, we directly compared the roles of location and sequential position in feature binding. Participants viewed a sequence of colored disks displayed at different locations, and were cued either by a disk's location or its ordinal position to report its remaining properties. The pattern of errors supported a mixed strategy with individual variation, suggesting that binding via either time or space could be used for this task.

Learning hierarchical sequence representations across human cortex and hippocampus

Sensory input arrives in continuous sequences that humans experience as segmented units, e.g., words and events. The brain’s ability to discover regularities is called statistical learning. Structure can be represented at multiple levels, including transitional probabilities, ordinal position, and identity of units. To investigate sequence encoding in cortex and hippocampus, we recorded from intracranial electrodes in human subjects as they were exposed to auditory and visual sequences containing temporal regularities. We find neural tracking of regularities within minutes, with characteristic profiles across brain areas. Early processing tracked lower-level features (e.g., syllables) and learned units (e.g., words), while later processing tracked only learned units. Learning rapidly shaped neural representations, with a gradient of complexity from early brain areas encoding transitional probability, to associative regions and hippocampus encoding ordinal position and identity of units. These findings indicate the existence of multiple, parallel computational systems for sequence learning across hierarchically organized cortico-hippocampal circuits.

Regulatory factors influence grapheme-color associations in synesthete and non-synesthetes: a review and model

Grapheme-color synesthetes experience linguistic symbols (e.g., letters of the alphabet) as having a consistent color (e.g., “The letter S is burgundy red”). Intriguingly, when non-synesthetes are forced to choose colors for letters, similar non-random distributions are observed. Why are certain letters likelier to be associated with certain colors? Researchers have long sought to explain these trends, and in the past few decades numerous studies have reported correlations between synesthetic colors and various properties of letters, such as ordinal position, frequency in the language, and even pronunciation. These influences, which we call “Regulatory Factors” (RFs), each explain some fraction of the variation in observed associations. In the present work, we provide an updated review of the literature, covering all known studies of RFs. We describe each RF and the operationalization that was used to measure it. For each RF, we also replicate the results in our own database of synesthetes and non-synesthetes, in some cases testing for the first time whether the RF influences the associations of non-synesthete controls. Finally, we introduce a new statistical model of synesthetic associations, that can evaluate the effect of all RFs in a single model.

Dissociated neural representations of content and ordinal structure in auditory sequence memory

When retaining a sequence of auditory tones in working memory (WM), two forms of information – frequency (content) and ordinal position (structure) – have to be maintained in the brain. Here, we employed a time-resolved multivariate decoding analysis on content and structure information separately to examine their neural representations in human auditory WM. We demonstrate that content and structure are stored in a dissociated manner and show distinct characteristics. First, each tone is associated with two separate codes in parallel, characterizing its frequency and ordinal position, respectively. Second, during retention, a structural retrocue reactivates structure but not content, whereas a following white noise triggers content but not structure. Third, structure representation remains unchanged whereas content undergoes a transformation throughout memory progress. Finally, content reactivations during retention correlate with WM behavior. Overall, our results support a factorized content-structure representation in auditory WM, which might help efficient memory formation and storage by generalizing stable structure to new auditory inputs.

Cumulative semantic interference across unrelated responses in school-age children's picture naming

Naming semantically related images results in progressively slower responses as more images are named. There is considerable documentation in adults of this phenomenon, known as cumulative semantic interference. Few studies have focused on this phenomenon in children. The present research investigated cumulative semantic interference effects in school-aged children. In Study 1, children named a series of contiguous, semantically related pictures. The results revealed no cumulative interference effects. Study 2 utilized an approach more closely aligned with adult methods, incorporating intervening, unrelated items intermixed with semantically related items within a continuous list. Study 2 showed a linear increase in reaction time as a function of ordinal position within semantic sets. These findings demonstrate cumulative semantic interference effects in young, school-aged children that are consistent with experience-driven changes in the connections that underlie lexical access. They invite further investigation of how children's lexical representation and processing are shaped by speaking experiences.

Numerical ordinality in a wild nectarivore

Ordinality is a numerical property that nectarivores may use to remember the specific order in which to visit a sequence of flowers, a foraging strategy also known as traplining. In this experiment, we tested whether wild, free-living rufous hummingbirds ( Selasphorus rufus ) could use ordinality to visit a rewarded flower. Birds were presented with a series of linear arrays of 10 artificial flowers; only one flower in each array was rewarded with sucrose solution. During training, birds learned to locate the correct flower independent of absolute spatial location. The birds' accuracy was independent of the rewarded ordinal position (1st, 2nd, 3rd or 4th), which suggests that they used an object-indexing mechanism of numerical processing, rather than a magnitude-based system. When distance cues between flowers were made irrelevant during test trials, birds could still locate the correct flower. The distribution of errors during both training and testing indicates that the birds may have used a so-called working up strategy to locate the correct ordinal position. These results provide the first demonstration of numerical ordinal abilities in a wild vertebrate and suggest that such abilities could be used during foraging in the wild.