NONRETINAL VISION: INDIVIDUAL DIFFERENCES

Nonretinal vision is a term for visual experience in the absence of visual stimulation (e.g., visual imagery, visual working memory, attentional templates). Many previous studies have found that humans can use nonretinal vision to influence visual perceptual task performance (e.g., holding the identity of an upcoming target in mind prior to visual search), but different studies have made vastly different conclusions about the extent of this influence. One issue is that individual differences in nonretinal vision are rarely taken into account, but they may greatly impact perception. For example, there is a wide spectrum of nonretinal visual vividness: on one end, there are people who cannot visualize even concrete objects (aphantasia). On the other end, some people have such strong nonretinal vividness that it interferes with visual perception on a daily basis, as in the case of synaesthesia (e.g., uncontrollably imagining colors attached to letters of the alphabet). The main goal of this project is to investigate the extent to which individual differences impact behavioral and cortical correlations between nonretinal vision and visual perception.

Visual Hallucinations

The most common example of nonretinal vision is visual imagery: we know from fMRI studies that visual imagery can recruit the same cortical structures as visual perception (Albers et al., 2013), and subjectively we can report seeing with our “mind’s eye” (Bértolo, 2005). If the experience of nonretinal vision appears to occur in the external environment rather than within the mind’s eye, it is called a visual hallucination (Pearson et al., 2016).

 

Visual hallucinations are rarely studied in an experimental setting. This is due to the experience being highly subjective, uncontrolled, and unpredictable (Pearson et al., 2016). Another major problem in studying hallucinations is that they are often confounded with comorbid conditions such as schizophrenia, Parkinson’s disease, or Alzheimer’s, or coupled with the consumption of mind-altering substances, making it impossible to research the exclusive experience of hallucinations in the brain. The goal of the current study is to induce the experience of visual hallucinations in healthy subjects; identify an association between visual imagery, perception, and hallucinations; and record the brain-oxygen-level-dependent (BOLD) signal associated with imagery and hallucination-proneness.

Our hypothesis is that individual differences in nonretinal visual abilities (such as imagery vividness) influences perceptual experience.

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If someone has vivid imagery but intact reality monitoring, they are not likely to experience hallucinations.

However, if reality monitoring is impaired, a person with vivid imagery may be more susceptible to experience a hallucination.

Whereas, even if a person with weak imagery has reality monitoring issues, they may be less likely to experience hallucinations because their imagery is not strong enough to confuse with perception.