title: An asymmetric outer retinal response to drifting sawtooth gratings.
abstract: Electroretinogram (ERG) studies have demonstrated that the retinal response to temporally modulated fast-ON and fast-OFF sawtooth flicker is asymmetric. The response to spatiotemporal sawtooth stimuli has not yet been investigated. Perceptually, such drifting gratings or diamond plaids shaded in a sawtooth pattern appear brighter when movement produces fast-OFF relative to fast-ON luminance profiles. The neural origins of this illusion remain unclear (although a retinal basis has been suggested). Thus we presented toad eyecups with sequential epochs of sawtooth, sine-wave, and square-wave gratings drifting horizontally across the retina at temporal frequencies of 2.5-20 Hz. All ERGs revealed a sustained direct-current (DC) transtissue potential during drift and a peak at drift offset. The amplitudes of both phenomena increased with temporal frequency. Consistent with the human perceptual experience of sawtooth gratings, the sustained DC potential effect was greater for fast-OFF cf. fast-ON sawtooth. Modeling suggested that the dependence of temporal luminance contrast on stimulus device frame rate contributed to the temporal frequency effects but could not explain the divergence in response amplitudes for the two sawtooth profiles. The difference between fast-ON and fast-OFF sawtooth profiles also remained following pharmacological suppression of postreceptoral activity with tetrodotoxin (TTX), 2-amino-4-phosphonobutric acid (APB), and 2,3 cis-piperidine dicarboxylic acid (PDA). Our results indicate that the DC potential difference originates from asymmetries in the photoreceptoral response to fast-ON and fast-OFF sawtooth profiles, thus pointing to an outer retinal origin for the motion-induced drifting sawtooth brightness illusion.
authors.affiliation: School of Psychology and Public Health, La Trobe University, Melbourne, Victoria, Australia; and Centre for Human Psychopharmacology, Swinburne University of Technology, Melbourne, Victoria, Australia.
authors.forename: Nina
authors.initials: N
authors.lastname: Riddell
authors.affiliation: Centre for Human Psychopharmacology, Swinburne University of Technology, Melbourne, Victoria, Australia.
authors.forename: Laila
authors.initials: L
authors.lastname: Hugrass
authors.affiliation: Centre for Human Psychopharmacology, Swinburne University of Technology, Melbourne, Victoria, Australia.
authors.forename: Jude
authors.initials: J
authors.lastname: Jayasuriya
authors.affiliation: School of Psychology and Public Health, La Trobe University, Melbourne, Victoria, Australia; and.
authors.forename: Sheila G
authors.initials: SG
authors.lastname: Crewther
authors.affiliation: Centre for Human Psychopharmacology, Swinburne University of Technology, Melbourne, Victoria, Australia dcrewther@swin.edu.au.
authors.forename: David P
authors.initials: DP
authors.lastname: Crewther
mesh_terms: D000818:Animals; D002024:Bufo marinus; D004596:Electroretinography; D005074:Evoked Potentials, Visual; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D008297:Male; D009903:Optical Illusions; D010775:Photic Stimulation; D010875:Pipecolic Acids / Q000494:pharmacology; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014796:Visual Perception
chemical_list: D018691:Excitatory Amino Acid Antagonists; D010875:Pipecolic Acids; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; C029262:2,3-piperidinedicarboxylic acid
keywords: brightness illusion; electroretinogram; flicker; motion; sawtooth; spatiotemporal