Discomfort and the cortical haemodynamic response to coloured gratings

Abstract

In five experiments we measured the amplitude of the haemodynamic response to visual patterns using near infrared spectroscopy of the visual cortex. The patterns were gratings with bars that differed in chromaticity but not in luminance. In all experiments, with a wide range of chromaticities of the grating bars, the amplitude of the haemodynamic response increased with the separation of the chromaticities in the CIE 1976 UCS diagram. The amplitude did not vary consistently with the cone activation, or with the signal in colour difference channels. In four further experiments, again with a wide range of chromaticities, the gratings were rated for visual comfort. Discomfort increased consistently with the separation of the chromaticities. Given that a large haemodynamic response to patterns is generally associated with headache, we suggest that the discomfort may be a homeostatic signal to reduce sustained metabolic load on the visual cortex.

Visual discomfort and the spatial distribution of Fourier energy

“…Coloured gratings with a large (and unnatural, Webster, Mizokami, and Webster, 2007) colour difference result in a high--amplitude haemodynamic response and are uncomfortable to view. The discomfort is proportional to the colour difference, as is the amplitude of the haemodynamic response (Haigh et al, 2013). Furthermore individuals who are particularly susceptible to visual discomfort, those experiencing migraine with aura, demonstrate an abnormally large haemodynamic response to uncomfortable visual stimuli (Cucchiara et al, 2014), an abnormality that is normalised when the stimulus is made more comfortable (Huang et al, 2011).…”

“…The signal is large for patterns that are uncomfortable (e.g., gratings with mid--range spatial frequency, i.e., around 3 cycles per degree --cpd) and is larger in individuals who are particularly susceptible to discomfort viz those with migraine (Huang, Cooper, Satana, Kaufman, and Cao, 2003). Metabolism is also reflected in the near infrared oxyhaemoglobin signal, and this is also larger for coloured patterns that are uncomfortable (Haigh et al, 2013). Haigh et al (2013) proposed that the discomfort is homeostatic and acts to prevent hypermetabolism.…”

“…Metabolism is also reflected in the near infrared oxyhaemoglobin signal, and this is also larger for coloured patterns that are uncomfortable (Haigh et al, 2013). Haigh et al (2013) proposed that the discomfort is homeostatic and acts to prevent hypermetabolism. If this is the case, one might expect images with 1/f spectra to be more comfortable than those with spectral slopes that depart from 1/f, irrespective of their content.…”

Cortical hyperexcitability and sensitivity to discomfort glare

“…Recently, evidence has emerged that visual scenes departing from natural image statistics result in higher visual discomfort (Fernandez and Wilkins, 2008;Juricevic et al, 2010), which is thought to be caused by hyperexcitability of neurons in response to unnatural stimuli (Juricevic et al, 2010). In agreement with this hypothesis, it has been found that discomfort ratings of different colored gratings correlate positively with the cortical haemodynamic response, as measured with near infrared spectroscopy (Haigh et al, 2013). High contrast, achromatic or colored gratings also cause a constriction of the pupil which has been linked to the level of cortical activity generated since these pupil response components remain even in the absence of damaged subcortical projections that abolish the light reflex response (Barbur, 2004;Wilhelm et al, 2002).…”

“…High contrast, achromatic or colored gratings also cause a constriction of the pupil which has been linked to the level of cortical activity generated since these pupil response components remain even in the absence of damaged subcortical projections that abolish the light reflex response (Barbur, 2004;Wilhelm et al, 2002). In the case of discomfort glare where high luminance sources are often used, hyperexcitability or saturation of a set of neurons is likely to occur; and as suggested by Wilkins and others (Haigh et al, 2013;Wilkins et al, 1984), the discomfort may be a homeostatic response, the purpose of which is to decrease the metabolic load. The current work employs glare sources with controlled levels of retinal illuminance and fMRI, in order to test whether discomfort glare is associated with hyperexcitability in different regions of the cortex.…”