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Contrast dependence of Vernier (VRN) displacement thresholds assessed by Steady-State Sweep VEP supports the hypothesis that magnocellular input to cortex underlies VRN performance

R. D Hamer F. A Carvalho; Dora Selma Fix Ventura; Annual Meeting of the Association for Research in Vision and Ophthalmology (51. 2010 Lauderdale, Florida)

Lauderdale, Florida: Association for Research in Vision and Ophthalmology, 2010 Anais

Lauderdale, Florida Association for Research in Vision and Ophthalmology 2010

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  • Título:
    Contrast dependence of Vernier (VRN) displacement thresholds assessed by Steady-State Sweep VEP supports the hypothesis that magnocellular input to cortex underlies VRN performance
  • Autor: R. D Hamer
  • F. A Carvalho; Dora Selma Fix Ventura; Annual Meeting of the Association for Research in Vision and Ophthalmology (51. 2010 Lauderdale, Florida)
  • Assuntos: ELETROFISIOLOGIA; CÓRTEX VISUAL; CÉLULAS DO GÂNGLIO RETINIANO
  • É parte de: Lauderdale, Florida: Association for Research in Vision and Ophthalmology, 2010 Anais
  • Descrição: Purpose:Primate magnocellular (M) ganglion cells appear to have higher spatial precision (with higher SNR) than parvocellular (P) cells, and the dependence of M cell spatial precision on contrast (C), SF, TF and stimulus velocity is more similar to human psychophysical performance than comparable data from P cells (Ruttiger et al, 2002; Sun et al., 2003, 2004). These authors hypothesize that M ganglion cells provide the retinal signal to cortex adequate to support vernier performance. We measured the C-dependence of cortical vernier (VRN) thresholds (thd) using the Sweep VEP (sVEP) to help evaluate this hypothesis. Methods:sVEP thds were measured in 12 young adults with normal vision. Vertical VRN breaks in colinearity were introduced to a horizontal squarewave grating (12.7x9.4o; 2 c/d; mean lum = 161 cd/m2), generating 6 moving + 6 static interleaved vertical columns of bars, for a total of 418 VRN breaks. The VRN stimulus alternated between aligned (grating w/o breaks) and misaligned (w/breaks) states at 6 Hz. During each of ten, 10-s trials, displacement (D) was swept logarithmically from 0.5\2019 to 7.5\2019. VRN thd was defined as the D at which the rising slope of the vector averaged 1F response extrapolated to zero mV. Cs tested: 4, 8, 16, 32, 64, 80%. Results:(1) Log VRN thd decreased linearly with log C with a slope of -0.5. (2) For C 16% , thds were hyperacuities (<1\2019). At high C, mean thd was 0.37\2019. (3) Thds for 2F had a different C-dependence, with little effect of C 16%. Thds for 2F were < 1F thds below 16% C, but were 1F thds beyond 16%. (4) The slopes of the sVEP extrapolation lines for 1F were 2-3 times > 2F slopes. (5) In a control protocol, symmetric, bidirectional displacements only generated 2F responses. (6) When the static and moving columns of bars had different Cs (16% moving; variable C static), a 1F response occurred when the static-bar C was as low as 1-2% C.
    No 1F occurred when the static bar had 0% C. Conclusions:Results 3-5 imply that the 1F and 2F components derive from distinct neurons, and support the notion that 2F responses reflect symmetric cortical motion responses. The C-dependence of sVEP VRN (1F) thresholds is similar to prior psychophysics, and recapitulates M-cell C-dependence (Wehrhahn & Westheimer, 1990; Sun et al., 2003, 2004). Results 1 and 6 support the hypothesis that cortex extracts relative position information with hyperacuity precision preferentially from M cell signals
  • Editor: Lauderdale, Florida Association for Research in Vision and Ophthalmology
  • Data de criação/publicação: 2010
  • Formato: p. E-abstract 1498.
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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