title: Contrast sensitivity in seasonal and nonseasonal depression.
abstract: BACKGROUND
  Psychophysics has been used for the early diagnosis of many diseases that affect the visual pathway including those not usually considered vision-related (e.g., Parkinson's disease). Little has been done, however, to investigate visual functioning in psychological disorders known to be effectively treated by phototherapy. We measured the static and dynamic spatial contrast detection thresholds of seasonally depressed (SAD), nonseasonally depressed (Depressed) and nondepressed (Control) individuals.
  
  
  METHODS
  Two psychophysical experiments which measured luminance contrast detection thresholds were conducted. Experiment 1 presented static, vertically oriented Gabors with center spatial frequencies ranging from 0.3 to 12.0 cpd (cycles per degree). Experiment 2 presented 0.5, 1.5 and 4.0 cpd Gabors whose phases were sinusoidally reversed at 2.0, 4.0, 8.0, 16.0, and 32.0 c/s (Hz).
  
  
  RESULTS
  SAD showed significantly greater contrast sensitivities than Controls for static spatial frequencies equal to or greater than 6.0 cpd. Depressed showed significantly greater contrast sensitivities at 6.0 cpd and 12.0 cpd. With phase modulation, the SAD group showed significantly enhanced contrast sensitivity with 4.0 cpd-2.0 Hz Gabors. All other results at lower spatial-higher temporal frequencies were not significant.
  
  
  CONCLUSIONS
  Most of the subjects were drawn from the student population instead of the community or clinics, even though they met the criteria for clinical depression. Antidepressant use was not controlled for among the subjects.
  
  
  CONCLUSIONS
  These findings suggest that clinical depression can enhance contrast sensitivity when stimuli elicit strong parvocellular responses. These enhancements implicate differences in retinal functionality. Mechanisms that link neuromodulatory activity to retinal signal processing are proposed.
authors.affiliation: Lakehead University, Department of Psychology, Thunder Bay, Canada ON P7B 5E1. micheal.wesner@lakeheadu.ca
authors.forename: Michael F
authors.initials: MF
authors.lastname: Wesner
authors.forename: Josephine
authors.initials: J
authors.lastname: Tan
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015350:Contrast Sensitivity / Q000502:physiology*; D003863:Depression / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation; D011601:Psychophysics / Q000379:methods*; D012160:Retina / Q000503:physiopathology; D016574:Seasonal Affective Disorder / Q000503:physiopathology*; D014584:User-Computer Interface