Abstract
We explored whether two visual mental imagery experiences may be differentiated by electroencephalographic (EEG) and performance interactions with concurrent orienting external attention (OEA) to stimulus location and subsequent visuospatial detection. We measured within-subject (N = 10) event-related potential (ERP) changes during out-of-body imagery (OBI)—vivid imagery of a vertical line outside of the head/body—and within-body imagery (WBI)—vivid imagery of the line within one’s own head. Furthermore, we measured ERP changes and line offset Vernier acuity (hyperacuity) performance concurrent with those imagery, compared to baseline detection without imagery. Relative to OEA baseline, OBI yielded larger N200 and P300, whereas WBI yielded larger P50, P100, N400, and P800. Additionally, hyperacuity dropped significantly when concurrent with both imagery types. Partial least squares analysis combined behavioural performance, ERPs, and/or event-related EEG band power (ERBP). For both imagery types, hyperacuity reduction correlated with opposite frontal and occipital ERP amplitude and polarity changes. Furthermore, ERP modulation and ERBP synchronizations for all EEG frequencies correlated inversely with hyperacuity. Dipole Source Localization Analysis revealed unique generators in the left middle temporal gyrus (WBI) and in the right frontal middle gyrus (OBI), whereas the common generators were in the left precuneus and middle occipital cortex (cuneus). Imagery experiences, we conclude, can be identified by symmetric and asymmetric combined neurophysiological-behavioural patterns in interactions with the width of attentional focus.
Highlights
Dipole source localization analysis (DSLA) supports the notion that imagery is a higher cognitive function with strong asymmetric cortical substrates; these results suggest that the two imagery experiences considered here can be differentiated on the basis of their distinct lateralized functional organization
Here is the ‘adaptation’ of Falasca et al.’s model, within-body imagery (WBI) involved additional top-down components originating from the left temporal lobe to the posterior parietal lobe. The latter activation circuitry may explain why there was no event-related potential (ERP) evidence of interference between WBI and external orienting attention (EOA) since the left-specialized stream of processing might have run in parallel and independently of the contralateral one supporting broad attentional focus in orienting external attention (OEA)
This study shows that two types of phenomenologically distinct imagery types, which we have dubbed out-of-body imagery (OBI) and within-body imagery (WBI), can be distinguished and are associated by different neural patterns
Summary
Visual mental images have been defined as representations that are physically implemented in the brain as neural patterns without corresponding environmental external/exogenous stimulation to the retina [1,2,3] They may be generated from a single or a mixture of many types of sensory, perceptual, and cognitive processes and may include preparatory visual templates, information maintenance and manipulation in visual working memory as well as retrieval from long-term memory—These are all conditions that fit the traditional concept of ‘imagery’ (see [4] and review by [5]). This family of out-of-body imagery experiences is deemed to correspond to organized topographic cortical maps that objectively code the measurable physical properties of the external visual space (e.g., texture, color, luminance, contrast)
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