Visual Psychophysics / Physiological Optics - ARVO

More documents

Recommendations

Info

ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group – Visual Psychophysics / Physiological OpticsPurpose: The luminance flicker pathway is typically conceived of asa simple additive combination of M- and L-cone signals. As wereported before (ARVO, 2001), this simple picture is complicated bythe existence of multiple cone signals with different delays and signs,which can be revealed by most conditions of chromatic adaptation.Here, we extend these measurements and model the results in termsof an inhibitory surround network.Methods: Cone delays were measured by a flicker photometriccancellation technique. Human subjects varied the relative delaybetween two superimposed flickering lights (and their relativemodulation) in order to minimize or null the perception of flicker.One flickering light was either an M-cone or an L-cone isolatingstimulus, and the other was a “standard” light that was of the samewavelength as the background. Measurements were made as afunction of temporal frequency from 2.5 to about 25 Hz on a series ofadapting backgrounds with wavelengths between 410 and 658 nmand at several background intensities.Results: Under most conditions, sizeable delays or advances by asmuch as 33 ms have to be introduced between the M- or L-coneflickering light and the standard in order to null the perception offlicker, particularly when M-cone flicker is used. In general, theresults are consistent with the L- and M-cone signals being made upof faster components combined with delayed ones of the same oropposite sign. For M-cone signals, the delayed components can belarger than the fast, so that they predominate.Conclusions: These results challenge the idea that the luminancechannel is made up of only additive M- and L-cone inputs. However,these complexities may simply reflect the fact that the inhibitorysurround of each cone has both L- and M-cone inputs, and that thereare typically more L-cone inputs than M. We model the surround as anetwork of direct and indirect inhibitory lateral connections acrosswhich each step in the network inverts and delays the signal. Thus,the effective sign and overall delay of the slow signal depend uponthe relative strengths of the inhibitory feedback at each step and uponthe number of steps.Commercial Relationships: Andrew Stockman, NoneSupport: BBSRC410 Spatial Vision, Visual Psychophysics and Aging IIWednesday, May 08, 2013 8:30 AM-10:15 AMTCC LL 4/5 Paper SessionProgram #/Board # Range: 4063-4068Organizing Section: Visual Psychophysics / Physiological OpticsProgram Number: 4063Presentation Time: 8:30 AM - 8:45 AMTwo-point detection and appearance in the absence of higherorder aberrationsHeidi J. Hofer, Darren E. Koenig. College of Optometry, Universityof Houston, Houston, TX.Purpose: We investigated the impact of the cone mosaic onspatiochromatic reconstruction of two-point stimuli by measuringdetection and appearance with stimuli made smaller than retinalcones with adaptive optics. We sought to determine whetherdetection and perception of these points are independent near thefovea, as has been previously hypothesized, and if not the extent ofsummation for detection and color. We also investigated whethertwo-point resolution is consistent with a photoreceptor limit underthese conditions.Methods: We performed two experiments in which subjects viewed550nm two-point stimuli through a 6mm pupil with adaptive opticsaberration correction. Stimuli were viewed at ~1 degree eccentricityunder a rod bleaching protocol to isolate cone responses. In oneexperiment two subjects were shown either one or two spots (25 ms,0.5 arcmin estimated retinal full-width at half maximum (fwhm)) ofdifferent intensities and reported the number seen and colorappearance. Separation was varied from 1.5 to 15 arcmin. In thesecond experiment two subjects were shown either one or two dim,yet suprathrehsold, spots (15 ms, 0.5 and 1.1 arcmin estimated fwhm)and reported whether they believed one or two spots were present.Separation was varied from 0.5 to 12 arcmin.Results: Detection thresholds in the first experiment were consistentwith complete spatial summation up to 3-4 arcmin. Detection, but notcolor appearance, was independent for separations of 8 arcmin ormore and consistent with at least 15 arcmin of spatial uncertainty. Fortwo-point stimuli color appearance was highly variable, as for singlepoints, but also highly coupled. Both points were reported to have thesame color appearance on over 97% of trials, regardless ofseparation. Resolution thresholds were similar in both experiments,2.5-5 arcmin, with a slight tendency towards lower thresholds withthe larger spots.Conclusions: Cone detection at 1 degree is consistent with completespatial summation over an extent including at least a cone and itsnearest neighbors, creating challenges in recovering ‘single cone’sensations from the responses to tiny stimuli. Despite this extent,two-point resolution is roughly consistent with expectations based ona photoreceptor limit. The large variation, but lack of independence,in the color appearance of the two-point stimuli, implies nonlocalityin the color reconstruction mechanisms.Commercial Relationships: Heidi J. Hofer, None; Darren E.Koenig, NoneSupport: ROI EY019069, P30 EY07551Program Number: 4064Presentation Time: 8:45 AM - 9:00 AMA Comparison of Acuity and Cone Density in the TemporalRetinaNancy J. Coletta 1 , Toco Y. Chui 2 , Ann E. Elsner 2 . 1 Vision Science,New England College of Optometry, Boston, MA; 2 School ofOptometry, Indiana University, Bloomington, IN.Purpose: Cone spacing has long been thought to set a limit on visualacuity. While parafoveal acuity and cone density decrease at parallelrates with increasing myopia (Coletta and Watson, Vis Res, 2006;Chui et al., IOVS, 2008), parafoveal acuity has been reported toexceed the limit estimated from histological measures of conespacing (Williams and Coletta, JOSA A, 1987). Recent advances inretinal imaging allow a comparison of acuity and cone spacing in thesame eyes. We compared parafoveal acuity to cone density in severalyoung adult individuals to determine whether acuity is matched to thelimit estimated from cone density.Methods: Measurements were made on five subjects with an averageage of 28 years +/- 4.30 s.d., average spherical equivalent refractiveerror of -1.93 D +/- 3.32 s.d. and average axial length of 24.48 mm+/- 1.38 s.d. (IOL Master, Zeiss Meditec). Acuity was measured onthe temporal retinal meridian using 543 nm laser interference fringesat a retinal illumination of 100 td; fringes were displayed in a 1 degpatch at 2 deg and a 2 deg patch at 7 deg eccentricity. Acuity wasestimated at the 75% correct level for a 2AFC vertical/horizontaldiscrimination task. Cone densities in the temporal retinal meridianwere assessed using a second generation Adaptive Optics ScanningLaser Ophthalmoscope. Densities were measured at a nominal 630and 2070 microns from the foveal center with custom software(Matlab, Mathworks). Axial lengths were used to correct the conesampling positions and retinal area, as well as to convert conedensities to Nyquist frequencies (NF) in units of c/deg.©2013, Copyright by the Association for Research in Vision and Ophthalmology, Inc., all rights reserved. Go to iovs.org to access the version of record. For permissionto reproduce any abstract, contact the ARVO Office at arvo@arvo.org.
ARVO 2013 Annual Meeting Abstracts by Scientific Section/Group – Visual Psychophysics / Physiological OpticsResults: The average acuity at 2 deg and 7 deg locations was 34.4c/deg +/- 3.54 s.e.m. and 17.62 c/deg +/- 2.33 s.e.m., respectively,while the average cone NFs at 2 deg and 7 deg locations were 26.97c/deg +/- 1.02 s.e.m. and 18.79 c/deg +/- 0.73 s.e.m., respectively.Individual ratios of acuity: cone NF ranged from 1.03 to 1.47 with amean of 1.26 at 2 deg and 0.75 to 1.18 with a mean of 0.93 at 7 deg.A paired t-test of acuity and cone NF values at 7 deg was notstatistically significant.Conclusions: Visual acuity exceeded the cone NF at 2 degeccentricity, confirming earlier studies that compared parafovealacuity and histological measures from different eyes. However ourresults at 7 deg eccentricity suggest that interferometric acuity mayprovide a good estimate of cone density in the perifoveal region.Commercial Relationships: Nancy J. Coletta, None; Toco Y.Chui, None; Ann E. Elsner, Aeon Imaging, LLC (I), Aeon Imaging,LLC (F), Aeon Imaging, LLC (P)Support: NIH Grants NEI EY007624 (AE Elsner), NEI EY004395(SA Burns), NEI P30EY019008 at IU and NEI R24 EY014817 atNECOProgram Number: 4065Presentation Time: 9:00 AM - 9:15 AMAge-related variation in foveal, parafoveal and peripheral spatialsuppressionRigmor C. Baraas, Craig Aaen-Stockdale, Stuart J. Gilson.Optometry & Visual Science, Buskerud University College,Kongsberg, Norway.Purpose: The study investigated motion-related spatial suppressionacross different age groups and across different eccentricities, withthe stimuli scaled according to the size of MT receptive fields. Theaim was to test three alternative hypotheses: If spatial suppression (1)is a perceptual correlate of center-surround antagonism in corticalvisual area V5 then the levels of spatial suppression should beconstant at all eccentricities; (2) reduces with increasing age, as aresult of a generalized weakening of inhibition then suppressionshould be lower for older observers, but constant at all eccentricities;(3) is related to contrast-related changes in receptive field size at aretinal level then suppression should vary with eccentricity andpossibly vary with cone density.Methods: Eleven normal, healthy subjects (7 females) with noknown ocular abnormalities, aged 21-71 yrs participated in the study.Their left eye was patched and they fixated a fixation cross presentedon the screen at eccentricities of 0, 2, 5 or 10 deg, or a back-litfixation point at 25 or 40 deg. The stimulus was a 2 Hz driftingsinusoidal grating with a peak contrast of 92%. Spatial frequency wasvaried with eccentricity to keep it close to peak contrast sensitivity.Stimulus duration was varied to derive a duration threshold. Highresolutionimages of the cone mosaic were obtained with theKongsberg Adaptive Optics Ophthalmoscope II.Results: Older observers showed zero suppression for foveal vision(0-2 deg), gradual increase in suppression in the parafovea (5-10 degeccentricity) and weaker suppression in the periphery (25-40 deg).Contrary to this, young observers showed strong suppression forfoveal and parafoveal vision (0-5 deg) with a gradual decline insuppression from 10 deg. There was between-individual variation inboth spatial suppression and cone density. Initial analyses indicatethat lower levels of suppression correlate with lower cone count.Conclusions: The strength of suppression, in both young and oldobservers, varied with eccentricity, despite the scaling of the stimuluswith average MT receptive field size. The results for older observersimply that weaker suppression is not a generalizable result. Theresults suggest that spatial suppression may be the result of low-levelstimulus characteristics and structural variation in the retina ratherthan a direct result of center-surround antagonism in MT.Commercial Relationships: Rigmor C. Baraas, None; CraigAaen-Stockdale, None; Stuart J. Gilson, NoneSupport: The Research Council of Norway Yggdrasil internationalmobility grant #211313 (CAa-S); Research Council of Norway Grant176541/V10 and 182768/V10 (RCB)Program Number: 4066Presentation Time: 9:15 AM - 9:30 AMHeterochromatic Modulation Photometry can be used to measureMacular Pigment Optical DensityCord R. Huchzermeyer 1 , Juliane Schlomberg 1 , Ulrich Welge-Lüssen 1 ,Tos TJM Berendschot 2 , Jan J. Kremers 1 . 1 Department ofOphthalmology, University Erlangen-Nuremberg, Erlangen,Germany; 2 University Eye Clinic, Maastricht, Netherlands.Purpose: Macular pigment optical density (MPOD) can be measuredpsychophysically by comparing the luminance ratio between a shortwavelengthand a long-wavelength light at a central and a peripheralretinal locus using heterochromatic flicker photometry (HFP).Heterochromatic modulation photometry (HMP) is a psychophysicaltest that uses, in contrast to HFP, test fields with constant meanluminance and chromaticity.To study whether HMP is suitable for measuring MPOD, wecompared a custom made HMP protocol with measurements usingHFP and macular pigment reflectometry (MPR).Methods: We developed a protocol for the measurement of MPODusing a Maxwellian view LED stimulator. Two lights (B: 460nm andR:660nm, retinal illuminance of 21 phot Td each) were modulated incounterphase in a 2° center-field surrounded by a 12° whitebackground (587 phot Td). Flicker detection threshold contrasts weredetermined for 9 different contrast ratios (B/R) of the two lights,varying between 10 -1 and 10 1 . Thresholds were determined using tworandomly interleaved staircases and a 2AFC (flicker/no flicker)procedure. The measurements were repeated with central and with 6°nasal fixation.For comparison, MPOD was also measured using an HFP-basedMacular Densitometer (Macular Metrics, USA) and the MacularPigment Reflectometer (Maastricht Instruments bv, TheNetherlands).The right eyes of 14 normal subjects were measured.Results: Log sensitivity (1/threshold) vs log B/R can be described bya V-shaped curve with a minimum at log B/R = 0 for the standardobserver with V λ -like spectral luminosity. A horizontal shift (alongthe log B/R axis) of the minimum represents a deviation from the V λ .The difference of the positions of the minima measured at central and6°nasal fixation were used to estimate the MPOD.MPOD measurements using HMP correlated with HFP (n=12,r=0.79, p
Page 5 and 6:
ARVO 2013 Annual Meeting Abstracts
Page 8 and 9:
Page 10 and 11:
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39: ARVO 2013 Annual Meeting Abstracts
Page 130: ARVO 2013 Annual Meeting Abstracts
show all

Visual Psychophysics / Physiological Optics - ARVO

Create successful ePaper yourself

Delete template?

Save as template?