September 2005
Volume 5, Issue 8
Free
Vision Sciences Society Annual Meeting Abstract  |   September 2005
A comparison of the BOLD fMRI response to achromatic, L/M opponent and S-cone opponent cardinal stimuli in human visual cortex: I. perceptually matched vs contrast matched stimuli
Author Affiliations
  • Kathy T. Mullen
    McGill Vision Research, Dept of Ophthalmology, McGill University, Canada
  • Serge O. Dumoulin
    McGill Vision Research, Dept of Ophthalmology, McGill University, Canada
  • Katie L. McMahon
    Centre for Magnetic Resonance, University of Queensland, Australia
  • Martina Bryant
    Centre for Magnetic Resonance, University of Queensland, Australia
  • Greig I. de Zubicaray
    Centre for Magnetic Resonance, University of Queensland, Australia
  • Robert F. Hess
    McGill Vision Research, Dept of Ophthalmology, McGill University, Canada
Journal of Vision September 2005, Vol.5, 95. doi:10.1167/5.8.95
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      Kathy T. Mullen, Serge O. Dumoulin, Katie L. McMahon, Martina Bryant, Greig I. de Zubicaray, Robert F. Hess; A comparison of the BOLD fMRI response to achromatic, L/M opponent and S-cone opponent cardinal stimuli in human visual cortex: I. perceptually matched vs contrast matched stimuli. Journal of Vision 2005;5(8):95. doi: 10.1167/5.8.95.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Aims: Our primary aim was to compare the responsiveness of the different visual cortical areas to stimulation of the two cone opponent systems and the achromatic system. The appropriate contrast metric for the comparison of color and luminance sensitivity is unknown, however, and so our secondary aim was to investigate whether equivalent fMRI responses of each cortical area could better be predicted from perceptual matches (in multiples of detection threshold) or a direct contrast match (in cone contrast).

Methods: MR images were acquired on a 4T Bruker MedSpec. Stimuli were sinewave counter-phasing rings (2Hz, 0.5cpd) cardinal for the selective activation of the L/M cone opponent (RG), S cone opponent (BY) and achromatic (Ach) systems. In different scans, stimuli were matched either at 25x detection threshold or in cone contrast (6%). We performed both stereotaxic and region of interest analyses on early visual areas (V1–V4v, and hMT+).

Results: For stimuli presented in multiples of detection threshold, BOLD responses in areas V1, V2, V3/VP and V4v are greatest for BY stimuli and weaker for both RG and achromatic stimuli, with the BY response significantly higher than the RG. For the same stimuli matched in cone contrast, the RG and BY response is similar in these areas. The averaged color response (RG & BY) was no different from the achromatic response with the exception of V1, which had a greater averaged color than achromatic response.

Conclusions: Perceptual visibility is not a good indicator of cortical activity across the RG, BY and achromatic mechanisms. fMRI BOLD signals are better predicted by cone contrast. Regardless of the metric, our data suggest a similar response to color (averaged RG & BY) and achromatic stimuli in V2, V3, VP and V4v. V1 shows a greater response to color, particularly with the cone contrast metric. Areas hMT+ and V3A do not follow these patterns and are discussed in a related abstract (Dumoulin et al).

Mullen, K. T. Dumoulin, S. O. McMahon, K. L. Bryant, M. de Zubicaray, G. I. Hess, R. F. (2005). A comparison of the BOLD fMRI response to achromatic, L/M opponent and S-cone opponent cardinal stimuli in human visual cortex: I. perceptually matched vs contrast matched stimuli [Abstract]. Journal of Vision, 5(8):95, 95a, http://journalofvision.org/5/8/95/, doi:10.1167/5.8.95. [CrossRef]
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