Li, S., Zeng, X., Shao, Z., & Yu, Q. (2023). Neural Representations in Visual and Parietal Cortex Differentiate between Imagined, Perceived, and Illusory Experiences. Journal of Neuroscience, 43(38), 6508–6524. https://doi.org/10.1523/jneurosci.0592-23.2023
* This article is based on this discussion of the literature.
Aphantasia, often referred to as “mind blindness,” describes a condition where individuals are unable to form mental images. While people with typical visual imagination can create vivid mental pictures, those with aphantasia experience a blank “mind’s eye.” Recent studies, including Neural Representations in Visual and Parietal Cortex Differentiate between Imagined, Perceived, and Illusory Experiences, help uncover the neural underpinnings of this phenomenon, offering insights into how the brain processes imagery, perception, and illusions.
Key Findings and Methods
In this study, researchers used advanced neuroimaging techniques—functional MRI (fMRI), eye-tracking, and multivariate decoding—to examine how different brain regions handle imagery, perception, and illusory experiences. Here are the main points from the findings:
Differentiating Imagined and Perceived Experiences:
• The parietal cortex showed a strong ability to represent imagined (internal) experiences, distinguishing them from external (perceived) ones.
• In contrast, early visual cortex (EVC) was more responsive to real perceptions than imagery. This difference suggests a specialized role of the parietal cortex in constructing internal experiences, even without external sensory input.
Imagery, Perception, and Illusion Representations:
• Illusions, which involve experiencing something not directly sensed, displayed neural representations closer to perception in the parietal cortex and more like imagery in the early visual cortex. This implies that parietal cortex processing plays a crucial role in interpreting and constructing subjective experiences.
Insights into Aphantasia:
• For individuals with aphantasia, the diminished representation in parietal cortex activity during imagery tasks might contribute to their inability to create visual images. This difference, particularly when comparing imagery and perception responses in the visual and parietal cortex, could be a critical neural basis for aphantasia.
Neural Processing: A Closer Look at the Brain Regions
Visual Cortex (Early Visual Cortex, EVC)
The early visual cortex is primarily activated by direct sensory input, which explains why real perceptions trigger strong responses here. However, its response weakens with imagery, as there’s no external stimulus.
Parietal Cortex
The parietal cortex plays a vital role in differentiating between internally generated (imagined) and externally derived (perceived) experiences. Its ability to maintain strong content-specific representations during imagery makes it a central component in constructing internal experiences. For aphantasic individuals, who lack visual imagery, this area may function differently, leading to difficulties in generating mental images.
Methodological Approach
The researchers’ methods involved comparing how these brain regions responded to tasks requiring perception, imagery, and illusion:
• fMRI Analysis: This tracked brain activity across visual and parietal cortices.
• Multivariate Decoding: This method helped identify patterns in brain activity, indicating that orientation representations were stronger during imagery in the parietal cortex but not in the EVC.
• Eye-Tracking: Controlled for differences in eye movements, ensuring that results were due to neural processing rather than external factors.
Practical Implications for Understanding Aphantasia
The findings of this study point to a domain-general role of the parietal cortex in internally generated experiences, shedding light on why people with aphantasia might struggle with mental imagery. By understanding how neural representations differ in those with and without mental imagery, researchers can gain further insights into the cognitive and neural architecture underlying aphantasia.
The study on neural representations between imagined, perceived, and illusory experiences advances our understanding of aphantasia. With aphantasia, differences in the parietal and visual cortex activity during imagery highlight that this mind blindness may stem from an altered ability to engage these brain regions for internal image generation. This research paves the way for deeper investigations into how our brains construct the rich internal world that many experience vividly and that some, due to aphantasia, may find challenging to envision.