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Modelling perception as a hierarchical competition differentiates imagined, veridical, and hallucinated percepts

DOI: 10.1101/2022.09.02.506121
Sulfaro, A. A., Robinson, A. K., & Carlson, T. A. (n.d.). Modelling perception as a hierarchical competition differentiates imagined, veridical, and hallucinated percepts. doi:10.1101/2022.09.02.506121

Abstract

Mental imagery is a process by which thoughts become experienced with sensory characteristics. Yet, it is not clear why mental images appear diminished compared to veridical images, nor how mental images are phenomenologically distinct from hallucinations, another type of non-veridical sensory experience. Current evidence suggests that imagination and veridical perception share neural resources. If so, we argue that considering how neural representations of externally-generated stimuli (i.e. sensory input) and internally-generated stimuli (i.e. thoughts) might interfere with one another can sufficiently differentiate veridical, imaginary, and hallucinatory perception. We here use a simple computational model of a serially-connected, hierarchical network with bidirectional information flow to emulate the primate visual system. We show that modelling even first-approximations of neural competition can more coherently explain imagery phenomenology than non-competitive models. Our simulations predict that, without competing sensory input, imagined stimuli should ubiquitously dominate hierarchical representations. However, with competition, imagination should dominate high-level representations but largely fail to outcompete sensory inputs at lower processing levels. To interpret our findings, we assume low-level stimulus information (e.g. in early visual cortex) contributes most to the sensory aspects of perceptual experience, while high-level stimulus information (e.g. towards temporal regions) contributes most to its abstract aspects. Our findings therefore suggest that ongoing bottom-up inputs during waking life may prevent imagination from overriding veridical sensory experience. In contrast, internally-generated stimuli may be hallucinated when sensory input is dampened or eradicated. Our approach can explain individual differences in imagery, along with aspects of daydreaming, hallucinations, and non-visual mental imagery.

Authors

  • Alexander A Sulfaro2
  • Amanda K. Robinson2
  • Thomas A. Carlson2

Understanding Mental Imagery: A New Perspective

Overview/Introduction

Mental imagery is the process by which our thoughts take on sensory characteristics, allowing us to "see" or "hear" things in our mind without any external stimuli. However, mental images often seem less vivid than real images, and they differ from hallucinations, which are also internally-generated but feel real. This study explores how mental imagery, real perception, and hallucinations can be distinguished by considering perception as a competitive process within the brain.

Methodology

The researchers used a computational model to simulate the primate visual system. This model consisted of a hierarchical network with layers that process information in both directions—upwards from sensory input and downwards from thoughts. By simulating different scenarios, the study examined how internally-generated (imagined) and externally-generated (real) stimuli interact and compete within this network.

Key Findings

  • Neural Competition: The study found that when there is no competing sensory input, imagined stimuli can dominate the brain's hierarchical representations. However, when real sensory input is present, it tends to dominate the lower levels of processing, which are responsible for sensory aspects of perception.
  • Imagery vs. Hallucinations: The findings suggest that ongoing sensory input during waking life prevents imagination from overtaking real sensory experiences. In contrast, hallucinations may occur when sensory input is reduced or absent, allowing internally-generated stimuli to dominate.
  • Individual Differences: The model explains variations in mental imagery vividness among individuals, such as in conditions like aphantasia (lack of mental imagery) and hyperphantasia (extremely vivid imagery).

Implications

  • Practical Applications: Understanding how mental imagery works can help in developing therapies for conditions like hallucinations and improve techniques in fields such as sports psychology, where visualization is used to enhance performance.
  • Broader Understanding: This model provides a framework for understanding how the brain processes different types of perceptual experiences and could lead to new insights into how we perceive the world.

Limitations

  • Model Simplifications: The study uses a simplified model that may not capture all the complexities of the brain's neural processes. Future research could explore more detailed simulations to validate these findings.
  • Assumptions: The model assumes that internally and externally-generated stimuli use the same neural pathways, which may not always be the case.
In conclusion, this research offers a new perspective on mental imagery by highlighting the role of neural competition in differentiating between imagined, real, and hallucinatory perceptions. Understanding these processes could have significant implications for both scientific research and practical ap...