An Investigation into the Effects of Temporary Visual Deprivation on Cortical Hyperexcitability, and Links with Multisensory Integration
Dublin Core
Title
An Investigation into the Effects of Temporary Visual Deprivation on Cortical Hyperexcitability, and Links with Multisensory Integration
Creator
Abbie Cochrane
Date
2018
Description
Cortical hyperexcitability is a state of highly increased neuronal activity in the brain. The current research is a novel investigation into the effects of short term temporary visual deprivation on cortical hyperexcitability and resultant aberrant visual experiences in non-migraineurs, migraine with aura, and migraine only participants. This research also assesses the link between cortical hyperexcitability and its effects on aberrant experiences across all senses; vision, audition, gustation, olfaction, and bodily sensations. Forty-three participants, including three migraine aura sufferers and three migraine only sufferers, completed the pattern glare test to induce and measure state-based cortical hyperexcitability under normal and temporary visual deprivation conditions, along with two questionnaire measures; the Cortical Hyperexcitability Index (version II; CHi-II), measuring trait-based cortical hyperexcitability; and the Multi-Modality Unusual Sensory Experiences Questionnaire, assessing aberrant experiences across senses. Results indicated no effect of temporary visual deprivation on cortical hyperexcitability, although migraine aura participants reported higher cortical hyperexcitability levels overall compared to migraine only and non-migraineurs. State-based pattern glare was not associated with unusual experiences in senses aside from olfactory, however the trait-based CHi-II was strongly correlated with unusual auditory, gustatory, and bodily sensations. Potential methodological and theoretical reasons for these results are discussed, alongside improvements and new directions for future research.
Subject
Cortical hyperexcitability, pattern glare, sensory hallucinations, temporary visual deprivation, migraine with aura
Source
Participants
Forty-three participants took part in this study, consisting of 28 females and 15 males. All participants were students at Lancaster University with a mean age of 22.5 years, ranging from 19 to 36 years (SD=2.92, SE=0.45). Twenty-two participants were native English speakers, and 21 spoke English as their second language. Of these participants, three self-reported suffering with migraine only (MO) and three with migraine with aura (MA). Participants were recruited using opportunity sampling, and all gave fully informed consent before completing the experiment.
Prior to participation, all participants were screened to ensure they did not suffer with any form of epilepsy, seizures of an unknown origin, and that they had not recently undergone brain or eye surgery. As no subjects reported these experiences, no participants were excluded on this basis. One participant reported suffering with micropsia; a visual impairment causing distortion of object size, so was removed from future analyses. All remaining participants reported normal or corrected to normal vision (i.e. through aid of glasses or contact lenses). Two participants were later removed from analysis for unusual scores on the baseline pattern glare task measure, explained in the results section. As such, the final sample size was 40 (age: M=22.53, SD=3.02, SE=0.48).
Materials and Procedure
Pattern glare task. Participants completed the pattern glare task under two conditions; blindfold or non-blindfold, creating a within-subjects design. Half completed the blindfold condition first, followed by the non-blindfold condition, with the other half completing the non-blindfold condition followed by the blindfold condition.
The pattern glare task utilised three black and white striped grating patterns. The low frequency grating, calculated to have a spatial frequency of 0.5 cycles per degree (cpd; Figure 1), and the high frequency grating of 5.8cpd (Figure 2) acted as baseline measures. The medium frequency was the critical triggering stimuli, with a grating of 2.5cpd (Figure 3). Stimuli measured 17.5cm by 13.5cm each and were presented on paper. They were placed on the wall at eye level 50cm from the participant, resulting in a visual angle of 15.4°.
Participants completed two trials; blindfold and non-blindfold. In the non-blindfold trial, participants were presented the three striped gratings, one at a time. Participants were asked to look at the grating for fifteen seconds, focusing on a central fixation point. If they found stimuli too aversive to view for the full time, they could inform the researcher, who would promptly remove the stimuli. There were 10 second intervals between presentations of gratings to allow the researcher to prepare the next stimulus. All stimuli were presented in a randomised order, to avoid order and carryover effects confounding results. After viewing each grating, participants completed a questionnaire consisting of seventeen items (Appendix A) asking about any visual distortions and discomforts experienced whilst viewing the stimuli, such as “shadowy shapes”, “colour distortions”, and “illusory stripes”. These are termed Associated Visual Distortions (AVDs). Each question was answered using a 7-point Likert scale assessing the intensity of each AVD experienced (0 = “not at all”, 6 = “extremely”). Responses were used to calculate a pattern glare score; a measure of state-based cortical hyperexcitability triggered by the stimuli. The blindfold condition followed a similar procedure, the only difference being that participants were required to wear a blackout blindfold for five minutes at the start of the trial before viewing only the medium and high frequency stimuli and answering the questionnaire as in the non-blindfold condition.
Whilst conducting the experiment, laboratory light conditions were controlled with blackout blinds covering all windows and relying on internal lighting controlled by the researcher. This prevented differences in intensity of light affecting how participants responded to the stimuli, particularly after removing the blindfold. Each pattern glare trial took approximately 10-15 minutes to complete. Additional questionnaire measures were carried out between the two pattern glare task trials, allowing a washout period for participants’ eyes to recover between viewings of uncomfortable stimuli, and excitability levels to return to normal. The full experiment took approximately 40 minutes to complete.
Figure 1. Stimuli with low frequency grating (0.5 cycles per degree) for pattern glare task.
Figure 2. Stimuli with high frequency grating (5.8 cycles per degree) for pattern glare task.
Figure 3. Stimuli with medium frequency grating (2.5 cycles per degree) for pattern glare task.
Questionnaire measures. Participants were asked to complete two different questionnaire measures; the Cortical Hyperexcitability Index version II (CHi-II; Fong et al., under review), and the Multi-Modality Unusual Sensory Experiences Questionnaire (MUSEQ; Mitchell et al., 2017).
Cortical Hyperexcitability Index version II (CHi-II). The CHi-II (Appendix B) is a trait-based proxy measure for assessing experiences thought to reflect cortical hyperexcitability. Measurements from the original CHi questionnaire (Braithwaite, Marchant, Takahashi, Dewe, & Watson, 2015) correlate with neurological measures of cortical hyperexcitability (Braithwaite, Mevorach, & Takahashi, 2015), suggesting CHi accurately and reliably measures cortical hyperexcitability.
The updated version (CHi-II) consists of 30 questions. Each item used a seven-point Likert response scale to rate participants’ unusual visual experiences in terms of frequency (0 = “never”, 6 = “all the time”) and intensity (0 = “not at all”, 6 = “extremely intense”). Experiences examined fall under three factors; Heightened Visual Sensitivity and Discomfort (HVSD), for example “irritation from indoor lights”; Aura-Like Hallucinatory Experiences (AHE), such as “flashes of moving shapes”; and Distorted Visual Perception, including “everyday objects look different”. Frequency and intensity scores for each question were added, making a maximum of twelve. The totals for each of the 30 items were summed to give a score of cortical hyperexcitability for each participant, with a maximum score of 360.
Multi-Modality Unusual Sensory Experiences Questionnaire (MUSEQ). The recently devised MUSEQ (Appendix C) measures unusual sensory experiences across six human senses: auditory, visual, olfactory, gustatory, bodily sensations, and sensed presence of others. Within each factor, questions range from broad sensory tricks (i.e. “my eyes have played tricks on me”) to hallucinatory experiences (i.e. “I have heard a person’s voice and found that no-one was there”), encompassing a range of more common to more unusual perceptual experiences. Questions used five-point Likert scales (0 = “never; never happened”, 4 = “frequently; at least monthly”).
As one item in the original MUSEQ was highly similar to an item in CHi-II, this was removed from the present version of MUSEQ used in the current study, in order to avoid conflation of results when comparing the two questionnaires.
Ethics statement
This research was ethically approved by the Departmental Ethics Committee at Lancaster University’s Department of Psychology on 11/05/2018.
Forty-three participants took part in this study, consisting of 28 females and 15 males. All participants were students at Lancaster University with a mean age of 22.5 years, ranging from 19 to 36 years (SD=2.92, SE=0.45). Twenty-two participants were native English speakers, and 21 spoke English as their second language. Of these participants, three self-reported suffering with migraine only (MO) and three with migraine with aura (MA). Participants were recruited using opportunity sampling, and all gave fully informed consent before completing the experiment.
Prior to participation, all participants were screened to ensure they did not suffer with any form of epilepsy, seizures of an unknown origin, and that they had not recently undergone brain or eye surgery. As no subjects reported these experiences, no participants were excluded on this basis. One participant reported suffering with micropsia; a visual impairment causing distortion of object size, so was removed from future analyses. All remaining participants reported normal or corrected to normal vision (i.e. through aid of glasses or contact lenses). Two participants were later removed from analysis for unusual scores on the baseline pattern glare task measure, explained in the results section. As such, the final sample size was 40 (age: M=22.53, SD=3.02, SE=0.48).
Materials and Procedure
Pattern glare task. Participants completed the pattern glare task under two conditions; blindfold or non-blindfold, creating a within-subjects design. Half completed the blindfold condition first, followed by the non-blindfold condition, with the other half completing the non-blindfold condition followed by the blindfold condition.
The pattern glare task utilised three black and white striped grating patterns. The low frequency grating, calculated to have a spatial frequency of 0.5 cycles per degree (cpd; Figure 1), and the high frequency grating of 5.8cpd (Figure 2) acted as baseline measures. The medium frequency was the critical triggering stimuli, with a grating of 2.5cpd (Figure 3). Stimuli measured 17.5cm by 13.5cm each and were presented on paper. They were placed on the wall at eye level 50cm from the participant, resulting in a visual angle of 15.4°.
Participants completed two trials; blindfold and non-blindfold. In the non-blindfold trial, participants were presented the three striped gratings, one at a time. Participants were asked to look at the grating for fifteen seconds, focusing on a central fixation point. If they found stimuli too aversive to view for the full time, they could inform the researcher, who would promptly remove the stimuli. There were 10 second intervals between presentations of gratings to allow the researcher to prepare the next stimulus. All stimuli were presented in a randomised order, to avoid order and carryover effects confounding results. After viewing each grating, participants completed a questionnaire consisting of seventeen items (Appendix A) asking about any visual distortions and discomforts experienced whilst viewing the stimuli, such as “shadowy shapes”, “colour distortions”, and “illusory stripes”. These are termed Associated Visual Distortions (AVDs). Each question was answered using a 7-point Likert scale assessing the intensity of each AVD experienced (0 = “not at all”, 6 = “extremely”). Responses were used to calculate a pattern glare score; a measure of state-based cortical hyperexcitability triggered by the stimuli. The blindfold condition followed a similar procedure, the only difference being that participants were required to wear a blackout blindfold for five minutes at the start of the trial before viewing only the medium and high frequency stimuli and answering the questionnaire as in the non-blindfold condition.
Whilst conducting the experiment, laboratory light conditions were controlled with blackout blinds covering all windows and relying on internal lighting controlled by the researcher. This prevented differences in intensity of light affecting how participants responded to the stimuli, particularly after removing the blindfold. Each pattern glare trial took approximately 10-15 minutes to complete. Additional questionnaire measures were carried out between the two pattern glare task trials, allowing a washout period for participants’ eyes to recover between viewings of uncomfortable stimuli, and excitability levels to return to normal. The full experiment took approximately 40 minutes to complete.
Figure 1. Stimuli with low frequency grating (0.5 cycles per degree) for pattern glare task.
Figure 2. Stimuli with high frequency grating (5.8 cycles per degree) for pattern glare task.
Figure 3. Stimuli with medium frequency grating (2.5 cycles per degree) for pattern glare task.
Questionnaire measures. Participants were asked to complete two different questionnaire measures; the Cortical Hyperexcitability Index version II (CHi-II; Fong et al., under review), and the Multi-Modality Unusual Sensory Experiences Questionnaire (MUSEQ; Mitchell et al., 2017).
Cortical Hyperexcitability Index version II (CHi-II). The CHi-II (Appendix B) is a trait-based proxy measure for assessing experiences thought to reflect cortical hyperexcitability. Measurements from the original CHi questionnaire (Braithwaite, Marchant, Takahashi, Dewe, & Watson, 2015) correlate with neurological measures of cortical hyperexcitability (Braithwaite, Mevorach, & Takahashi, 2015), suggesting CHi accurately and reliably measures cortical hyperexcitability.
The updated version (CHi-II) consists of 30 questions. Each item used a seven-point Likert response scale to rate participants’ unusual visual experiences in terms of frequency (0 = “never”, 6 = “all the time”) and intensity (0 = “not at all”, 6 = “extremely intense”). Experiences examined fall under three factors; Heightened Visual Sensitivity and Discomfort (HVSD), for example “irritation from indoor lights”; Aura-Like Hallucinatory Experiences (AHE), such as “flashes of moving shapes”; and Distorted Visual Perception, including “everyday objects look different”. Frequency and intensity scores for each question were added, making a maximum of twelve. The totals for each of the 30 items were summed to give a score of cortical hyperexcitability for each participant, with a maximum score of 360.
Multi-Modality Unusual Sensory Experiences Questionnaire (MUSEQ). The recently devised MUSEQ (Appendix C) measures unusual sensory experiences across six human senses: auditory, visual, olfactory, gustatory, bodily sensations, and sensed presence of others. Within each factor, questions range from broad sensory tricks (i.e. “my eyes have played tricks on me”) to hallucinatory experiences (i.e. “I have heard a person’s voice and found that no-one was there”), encompassing a range of more common to more unusual perceptual experiences. Questions used five-point Likert scales (0 = “never; never happened”, 4 = “frequently; at least monthly”).
As one item in the original MUSEQ was highly similar to an item in CHi-II, this was removed from the present version of MUSEQ used in the current study, in order to avoid conflation of results when comparing the two questionnaires.
Ethics statement
This research was ethically approved by the Departmental Ethics Committee at Lancaster University’s Department of Psychology on 11/05/2018.
Publisher
Lancaster University
Format
Data/Excel.xlsx
Identifier
Cochrane2018
Contributor
Rebecca James
Rights
Open
Relation
None
Language
English
Type
Data
Coverage
LA1 4YF
LUSTRE
Supervisor
Jason Braithwaite
Project Level
MSc
Topic
Neuropsychology
Sample Size
43 participants
Statistical Analysis Type
Correlations, t-tests, ANOVA, Bayesian Analysis
Files
Collection
Citation
Abbie Cochrane, “An Investigation into the Effects of Temporary Visual Deprivation on Cortical Hyperexcitability, and Links with Multisensory Integration,” LUSTRE, accessed April 25, 2024, https://www.johnntowse.com/LUSTRE/items/show/95.