Imagery in a pair of aphantasic and non-aphantasic identical twins: Neural similarities and differences
Abstract
Aphantasia is defined as a lack of voluntary visual imagery, with otherwise normal perception and visual recognition (Zeman et al., 2015). Aphantasics will often describe semantic but not perceptual detail when recalling visual stimuli (Bainbridge et al., 2021). However, the neural correlates that underpin this difference in visual recall remain largely unknown. To understand the neural correlates of aphantasia, we used fMRI to study a pair of identical twins (female, 31 years old) where one twin has typical visual imagery but the other has aphantasia as diagnosed by the Vividness of Visual Imagery Questionnaire and a drawing recall behavioral task. In the scanner, participants completed two visual imagery tasks - imagery for novel object and scene images and for familiar people and places (Bainbridge et al., 2020; Steel et al., 2021) – and a resting state scan to examine differences in functional connectivity. Both participants show anterior shifts in peak voxel activity for category-selective visual cortex during visual recall compared to perception, suggesting similar transformations of stimulus representations from encoding to recall. However, using whole-brain searchlight decoding, we found late perceptual and memory regions that differently decoded information from perception and recall between the two subjects, revealing differences in memory representations between aphantasia and typical imagery. A representational similarity analysis within those regions showed discriminable stimulus information during recall between both participants, which suggests some visual information is retrieved by the aphantasic twin during imagery. Overall, we see that the imager and aphantasic have different regions that share information across perception and recall, but both retain some level of visual information during recall, despite their different experiences.
Authors
- Deepasri Prasad1
- Emma Megla1
- Wilma A. Bainbridge3
Understanding Aphantasia: A Study of Identical Twins
Overview/Introduction
Methodology
- Participants: Two 31-year-old female identical twins, one with aphantasia and one with normal imagery.
- Tools: Functional Magnetic Resonance Imaging (fMRI) was used to observe brain activity.
- Tasks: Participants completed visual imagery tasks involving novel and familiar images, and their brain activity was compared during these tasks.
- Analysis: Researchers used various brain imaging analyses to compare the twins' brain activity patterns and connectivity.
Key Findings
- Visual Information in Memory: The aphantasic twin showed less visual information in memory than the imager twin, but more than expected, suggesting aphantasia might be a spectrum.
- Brain Activity Patterns: Both twins showed similar transformations of visual information from perception to recall, but different brain regions were involved.
- Functional Connectivity: The aphantasic twin had lower connectivity between certain brain regions, which might explain the reduced visual imagery.
- Unexpected Visual Information: Despite the lack of vivid imagery, the aphantasic twin retained some visual information in memory, especially for newly learned images.
Implications
- Understanding Memory and Perception: This study provides insights into how visual imagery and memory are processed differently in people with aphantasia.
- Spectrum of Aphantasia: The findings suggest that aphantasia may not be an all-or-nothing condition but rather exists on a spectrum.
- Potential for Diagnosis: Identifying neural markers for aphantasia could lead to better diagnostic tools and understanding of the condition.
Limitations
- Sample Size: The study focuses on a single pair of twins, which may limit the generalizability of the findings.
- Complexity of Brain Functions: The brain's complexity means that more research is needed to fully understand the nuances of aphantasia.