From Psy3241

Activation of the Striate Cortex in the absence of visual stimulation: an fMRI Study of Synesthesia- Presented by Hayley Devlin and Rachel Kimchi

Shadowed by Lauren Malonson and Meredith Walsh

Contents 1 Key Terms 2 Overview of Article 3 Results 4 Importance

Key Terms

Synesthesia-

This occurs when one sensory system in your body triggers a perceptual experience in another unrelated system. An common example of this is when a person hears a sound then will immediately see a color or shape in the mind's eye as a response to the sound. People who have synethesia are referred to as synethetes and are often unaware that there is anything wrong with them because it develops at such a young age. This is also the reason why researchers have a vague idea about how many people have synesthesia.

Primary Visual Cortex, Striate Cortex, V1

Located in the brain's occipital lobe, the primary visual cortex is part of the neocortex that receives visual input from the receptive cells of the retina.

Overview of Article

The purpose of this study was to find out if the primary visual cortex is activated without direct external input to the visual system. In other words, the question is, does the primary visual cortex play a functional role in internally generated visual perception? To determine this, an fMRI scan was conducted on a woman with color-word synesthesia (when she heard a word, she involuntarily saw a color) during two verbal tasks and control conditions. In the first task (passive listening), the participant was auditorily presented with 14 words, and in the next (verbal fluency), she was presented with one letter at a time and asked to generate as many words as possible starting with that letter. In the control conditions, tones were presented and the participant pressed a button when the frequency changed. All fMRI results were compared against those of normal participants.

Results

Results showed that V1 was activated in both the passive listening and the verbal fluency tasks in the participant with color-word synesthesia. The normal subjects did not show activation of V1 in any condition.

Importance

These results are significant for several reasons: first, while previous studies have tested the role of V1 in the presence of visual perception (in the absence of visual stimulation), those studies had mixed results; additionally, the previous studies focused on conscious visual perception, whereas this one focused on involuntarily generated perception; next, these results, as suggested in the study, may have important implications regarding other types of visualization that are uncontrolled by the experiencer (such as hallucinations); and finally, the results provide significant evidence that feedback connections into V1 may "mediate processes such as perceptual organization, attention and awareness," and that those connections play a major role in "associative and primary visual areas in visual experience" in the absence of direct visual stimulation.

See also: Synesthesia