March 2012
Volume 53, Issue 14
Free
ARVO Annual Meeting Abstract  |   March 2012
Mapping The Spatiotemporal (S-T) Domain And Gain Of Putative M- And P-dominated Limbs Of The Human Cortical Contrast Response Function (CRF) Using The Sweep Vep (svep)
Author Affiliations & Notes
  • Russell D. Hamer
    Departamento de Psicologia Experimental, Instituto de Psicologia, São Paulo, Brazil
    Smith-Kettlewell Eye Research Institute, San Francisco, California
  • Givago S. Souza
    Insituto de Ciencias Biologicas, Universidade Federal do Para, Belem, Brazil
    Nucleo de Medicina Tropical, Universidade Federal do Parã, Belem, Brazil
  • Thiago L. Costa
    Departamento de Psicologia Experimental, Instituto de Psicologia, São Paulo, Brazil
  • Bruno D. Gomes
    Insituto de Ciencias Biologicas, Universidade Federal do Para, Belem, Brazil
  • Luiz C. Silveira
    Insituto de Ciencias Biologicas, Universidade Federal do Para, Belem, Brazil
    Nucleo de Medicina Tropical, Universidade Federal do Parã, Belem, Brazil
  • Dora F. Ventura
    Departamento de Psicologia Experimental, Instituto de Psicologia, São Paulo, Brazil
  • Footnotes
    Commercial Relationships  Russell D. Hamer, None; Givago S. Souza, None; Thiago L. Costa, None; Bruno D. Gomes, None; Luiz C. Silveira, None; Dora F. Ventura, None
  • Footnotes
    Support  CAPES PROCAD 182/2007
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 5715. doi:
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      Russell D. Hamer, Givago S. Souza, Thiago L. Costa, Bruno D. Gomes, Luiz C. Silveira, Dora F. Ventura; Mapping The Spatiotemporal (S-T) Domain And Gain Of Putative M- And P-dominated Limbs Of The Human Cortical Contrast Response Function (CRF) Using The Sweep Vep (svep). Invest. Ophthalmol. Vis. Sci. 2012;53(14):5715.

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

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Abstract

Purpose: : Prior transient and steady-state VEP studies in humans and primates show the CRF frequently has two linear contrast (C) limbs (on log-C axes), a shallow limb at low C, and a steeper limb at high-C. These have been hypothesized to reflect M- and P-dominated responses, respectively (e.g., Nakayama & Mackeben, 1982; Souza et al., 2007). The presence of the 2 limbs, and the C at which they intersect, depends on the S-T and chromatic properties of the stimulus. The S-T domain of the 2 limbs has not yet been mapped in detail. This large S-T space can be mapped efficiently with the sVEP which requires 10-30 times less recording time (for equivalent SNR) than the transient VEP to obtain a CRF for one S-T combination. Our goal was to begin the process of generating a S-T map for achromatic CRFs using the sVEP.

Methods: : sVEP was recorded while presenting 2 or 10 c/d sinewave gratings (161 cd/m2 mean lum) phase-reversing at 6 Hz or 10 Hz; C increased logarithmically during each 10-s trial; vector average response at 2F1 was calculated for 8 sweeps/condition; lines were fit to the low- and high-C limbs of the CRF and extrapolated to 0 μV to estimate threshold (thd) for the putative M and P channels, respectively. C-gain (G) was estimated by converting the lines into linear-linear coordinates, and calculating the slope of the tangent line at the onset of the response (Kaplan & Shapley, 1986; KS86). 8 subjects were tested.

Results: : (1) Two-limbed CRFs were found at all S-T combinations. (2) At 6 Hz, the median P thd estimates were ~3.3x higher than the M thds. At 10 Hz, they were 5-11 times higher.(3) The ratio of putative M/P gains ranged from ~2 to 15 across all 4 conditions with a Md of ~2. (4) The C at which the low- and high-C limbs crossed was ~17% at 2 c/d, and ~30-40% at 10 c/d.

Conclusions: : These results are similar to those obtained with transient VEPs (Souza et al., 2007,2008). Result (2) is consistent with a relative enhancement of M sensitivity at higher TFs. The G-ratios (Result 3) from the 2 limbs of the CRFs are ~3-5 times smaller than the ratios from single M and P primate ganglion cells (KS86). The reasons for this difference need further investigation. The sVEP approach will permit efficient mapping of the S-T-C domain of the putative M- and P dominated components of the CRF.

Keywords: contrast sensitivity • visual cortex 
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