Abstract
Consistent semantic relations among objects (e.g., a toothbrush near a toothpaste) have been found to boost visual short-term memory. Perceptual similarity, particularly shared color, also benefits short-term memory for single-feature objects. This color-sharing bonus can be explained by a compression process that compacts redundant information to gain storage space. Here we aimed to investigate whether compression could offer a general account of both semantic- and color-sharing bonuses in visual short-term memory. If so, then color- and semantic-sharing effects should combine to boost accuracy, especially for unique items within displays including items that share color or meaning. Participants viewed scenes consisting of six objects. Scenes either included one semantically-related and/or perceptually-similar object pair plus four unrelated singleton objects, or six singleton objects in the baseline condition. Perceptually similar pairs shared their dominant color, while semantically related pairs included objects likely to co-occur in a realistic environment; in some trials, pairs were both perceptually similar and semantically related. Results showed that memory improved for scenes with a pair of perceptually-similar objects compared with baseline scenes, regardless of semantic similarity. The redundancy gain (memory for related vs. singleton objects) was only present for scenes with a pair of perceptually-similar objects. This pattern of result suggests that semantic grouping in combination with perceptual redundancy can improve memory due to redintegration, while compression arises from perceptual redundancy. According to these respective views, semantic groups can be represented only in long-term memory and the content of short-term memory remains unchanged, while only perceptual groups can change the nature of representations stored in short-term memory. Redintegration has been indeed previously proposed as an explanation of the superior recall of familiar items.