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Arash Sahraie, Sian Griffiths, Claire Conway; Comparison of pupil responses to the first and second order gratings. Journal of Vision 2008;8(6):946. doi: 10.1167/8.6.946.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Small, transient constrictions of the pupil are elicited by the onset of basic visual attributes such as colour, motion and luminance-defined gratings, as well as more complex stimuli such as faces. Evidence for cortical origins of such responses rely on attenuated responses measured after focal cortical lesions. We aimed to (a) establish whether similar responses are elicited by the onset of second order gratings; (b) in view of similarities/differences in psychophysical properties and neuronal processing of first and second order gratings, establish the similarities/differences in pupil responses as a function of spatial frequency, contrast and retinal eccentricity. Method: Gabor patches (spatial standard deviation, SSD = 2.5°; limited to ±2×SSD) with temporal smoothing (temporal standard deviation, TSD= 250ms; duration 4×TSD) were presented at a range of carrier frequencies, contrasts and eccentricities. Each block of testing contained randomly interleaved first and second order carriers. Pupil responses were measured in normal observers (n=6) using a modified ASL pupillometer and were analysed using P_trace software. Results/conclusions: We have demonstrated the existence of significant transient pupil constrictions elicited by the onset of second order gratings. The response amplitude to foveally presented first and second order gratings (2 cycles/°) varied monotonically with increasing grating contrast. Similar to previous reports, we showed that the pupil response amplitude to first order gratings varied systematically with spatial frequency within the range of frequencies tested (0.5–4.0 cycles/°). However, the second order gratings lacked similar frequency tuning properties. The shift to lower spatial frequencies for the peak pupil response to first order gratings as a function of retinal eccentricity mirrors that of the contrast sensitivity function. On the other hand, for second order gratings, there was only a general attenuation of response amplitude without a relative eccentricity dependent shift in peak sensitivity.
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