title: Optimization of large field tritan stimuli using concentric isoluminant annuli.
abstract: Large, nominally isoluminant chromatic gratings containing a short-wavelength component are prone to luminance contrast intrusions due to retinal inhomogeneity, especially as a result of the uneven distribution of macular pigment. Isoluminance is usually determined for a relatively small, central area, but a significantly larger stimulus cannot be isoluminant across the whole field, largely due to macular pigment absorption of short-wavelength light. This confounds attempts to maintain high selectivity, particularly in suprathreshold electrophysiological and brain-imaging studies that require large stimulus fields. Here we introduce the concept of a panisoluminant grating (PIG), which comprises a series of concentric annular regions, each adjusted to location-specific isoluminance for the observer. Gratings were modulated along subject-specific tritanopic confusion lines and the selectivity of responses to the PIG was tested according to both psychophysical and electrophysiological criteria. The psychophysically-determined temporal tuning function obtained using the PIG showed lower sensitivity and lower resolution than with a conventional tritan grating of equal diameter (18°). Chromatic onset visual evoked potentials (VEPs) to the PIG were dominated by a chromatic-specific negative wave and reduced achromatic response components that were prominent in VEPs to the conventional grating. These data demonstrate that a large tritan PIG is capable of eliciting selective responses of the S-cone-driven pathway at threshold and at suprathreshold levels. The PIG stimulus may prove beneficial in investigations that require large fields such as electrophysiological and brain imaging studies of chromatic processing.
authors.affiliation: University of Manchester Health Science Research Centre, Manchester Royal Eye Hospital, Manchester, UK. Neil.Parry@manchester.ac.uk
authors.forename: Neil R A
authors.initials: NR
authors.lastname: Parry
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Robson
mesh_terms: D000328:Adult; D003116:Color; D003118:Color Perception / Q000502:physiology*; D055253:Color Vision / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D010775:Photic Stimulation / Q000379:methods*; D011601:Psychophysics; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*