Vividness of visual imagery questionnaire scores and their relationship to visual short-term memory performance.

Mechanisms underlying visual imagery, the ability to create vivid mental representations of a scene in the absence of sensory input, remain to be fully understood. Some previous studies have proposed that visual imagery might be related to visual short-term memory (STM), with a common mechanism involving retention of visual information over short periods of time. Other observations have shown a strong relationship between visual imagery and functional activity in the hippocampus and primary visual cortex, both regions also associated with visual STM. Here we examined the relationship of visual imagery to STM and hippocampal and primary visual cortex volumes, first in a large sample of healthy people across a large age range (N = 229 behavioural data; N = 56 MRI data in older participants) and then in patients with Alzheimer's disease and Parkinson's disease (N = 19 in each group compared to 19 age-matched healthy controls). We used a variant of the "What was where?" visual object-location binding task to assess the quality of remembered information over short delays. In healthy people, no evidence of a relationship between the vividness of visual imagery and any visual STM performance parameter was found. However, there was a significant positive correlation between visual imagery and the volumes of the hippocampus and primary visual cortex. Although visual STM performance was significantly impaired in patients with Alzheimer's disease, their vividness of visual imagery scores were comparable to those of age-matched elderly controls and patients with Parkinson's disease. Despite hippocampal volumes also being reduced in Alzheimer's patients, there appeared to be no impact on their self-reported visual imagery. In conclusion, visual imagery was not significantly related to visual STM performance, either in healthy controls or Alzheimer's or Parkinson's disease but it was related to hippocampal and visual cortex volume in healthy people.

Impact of processing demands at encoding, maintenance and retrieval in visual working memory.

There has been surprisingly little examination of how recall performance is affected by processing demands induced by retrieval cues, how manipulations at encoding interact with processing demands during maintenance or due to the retrieval cue, and how these are affected with aging. Here, we investigate these relationships by examining the fidelity of working memory recall across two delayed reproduction tasks with a continuous measure of report across the adult lifespan. Participants were asked to remember and subsequently reproduce from memory the identity and location of a probed item from the encoding display. In Experiment 1, we examined the effect of filtering irrelevant information at encoding and the impact of filtering distracting information at retrieval simultaneously. In Experiment 2, we tested how ignoring distracting information during maintenance or updating current contents with new information during this period affects recall. The results reveal that manipulating processing requirements induced by retrieval cues (by altering the nature of the retrieval foil) had a significant impact on memory recall: the presence of two previously viewed features from the encoding display in the retrieval foil led to a decrease in identification accuracy. Although irrelevant information can be filtered out well at encoding, both ignoring irrelevant information and updating the contents of memory during the maintenance delay had a detrimental effect on recall. These effects were similar across the lifespan, but older individuals were particularly affected by manipulations of processing demands at encoding as well as increasing set size of information to be retained in memory. Finally, analyses revealed that there were no systematic relationships between filtering performance at encoding, maintenance and retrieval suggesting that these processing demands are independent of each other. Rather than filtering being a single, monolithic entity, the data suggest that it is better accounted for as distinctly dissociable cognitive processes that engage and articulate with different phases of working memory.

Recall cues interfere with retrieval from visuospatial working memory.

Visuospatial working memory allows us to hold multiple visual objects over short delays. It is typically tested by presenting an array of objects, then after a delay showing a 'probe' indicating which memory item to recall or reproduce by adjusting a target feature. However, recent studies demonstrate that information at the time of probe can disrupt recall. Here, in three experiments we test whether traditional memory probes, which contain features that compete with the feature to be recalled, may themselves interfere with performance. We asked participants to report the direction of one of the several coloured arrows in memory, based on its colour. First, we demonstrate that recall is better when the probe is initially just a coloured dot, rather than a coloured arrow which has to be adjusted to match orientation memory, consistent with interference from features of the probe itself. Second, this interference is present even when a mask follows the memory array, suggesting that the interference does not work by degrading immediate or iconic memory. Finally, when items are shown sequentially, the first and last items are invulnerable to probe interference. Our findings support recent theories of associative recall, in which probes reactivate features in WM, retrieving information by pattern completion.