Visual working memory in aphantasia: Retained accuracy and capacity with a different strategy.

Visual working memory paradigms involve retaining and manipulating visual information in mind over a period of seconds. Evidence suggests that visual imagery (sensory recruitment) is a strategy used by many to retain visual information during such tasks, leading some researchers to propose that visual imagery and visual working memory may be one and the same. If visual imagery is essential to visual working memory task performance there should be large ramifications for a special population of individuals who do not experience visual imagery, aphantasia. Here we assessed visual working memory task performance in this population using a number of different lab and clinical working memory tasks. We found no differences in capacity limits for visual, general number or spatial working memory for aphantasic individuals compared to controls. Further, aphantasic individuals showed no significant differences in performance on visual components of clinical working memory tests as compared to verbal components. However, there were significant differences in the reported strategies used by aphantasic individuals across all memory tasks. Additionally, aphantasic individual's visual memory accuracy did not demonstrate a significant oblique orientation effect, which is proposed to occur due to sensory recruitment, further supporting their non-visual imagery strategy reports. Taken together these data demonstrate that aphantasic individuals are not impaired on visual working memory tasks, suggesting visual imagery and working memory are not one and the same, with imagery (and sensory recruitment) being just one of the tools that can be used to solve visual working memory tasks.

The critical role of mental imagery in human emotion: insights from fear-based imagery and aphantasia.

One proposed function of imagery is to make thoughts more emotionally evocative through sensory simulation, which can be helpful both in planning for future events and in remembering the past, but also a hindrance when thoughts become overwhelming and maladaptive, such as in anxiety disorders. Here, we report a novel test of this theory using a special population with no visual imagery: aphantasia. After using multi-method verification of aphantasia, we show that this condition, but not the general population, is associated with a flat-line physiological response (skin conductance levels) to reading and imagining frightening stories. Importantly, we show in a second experiment that this difference in physiological responses to fear-inducing stimuli is not found when perceptually viewing fearful images. These data demonstrate that the aphantasic individuals' lack of a physiological response when imaging scenarios is likely to be driven by their inability to visualize and is not due to a general emotional or physiological dampening. This work provides evidence that a lack of visual imagery results in a dampened emotional response when reading fearful scenarios, providing evidence for the emotional amplification theory of visual imagery.

Sensory dynamics of visual hallucinations in the normal population.

Hallucinations occur in both normal and clinical populations. Due to their unpredictability and complexity, the mechanisms underlying hallucinations remain largely untested. Here we show that visual hallucinations can be induced in the normal population by visual flicker, limited to an annulus that constricts content complexity to simple moving grey blobs, allowing objective mechanistic investigation. Hallucination strength peaked at ~11 Hz flicker and was dependent on cortical processing. Hallucinated motion speed increased with flicker rate, when mapped onto visual cortex it was independent of eccentricity, underwent local sensory adaptation and showed the same bistable and mnemonic dynamics as sensory perception. A neural field model with motion selectivity provides a mechanism for both hallucinations and perception. Our results demonstrate that hallucinations can be studied objectively, and they share multiple mechanisms with sensory perception. We anticipate that this assay will be critical to test theories of human consciousness and clinical models of hallucination.