Psychology 3041/6014 Spring, 2014 1 of 5 FUNDAMENTAL VISUAL FUNCTIONS 1) Sensitivity a) Scotopic vs Photopic vision i) Scotopic ii) Photopic b) Dark adaptation i) Moving from light to dark ii) Chemical cycle of regeneration of rhodopsin c) Purkinje shift i) Rods react best to light of ~ 500 nm (blues) ii) Cones react best to light of ~550 nm (greens) iii) As vision shifts from photopic (cone) to scotopic (rod) vision, the sensitivity to different light wavelengths changes iv) Light at 500 nm (blue) becomes more bright (perceptually), and light at 550 nm (green) becomes less brightPsychology 3041/6014 Spring, 2014 2 of 5 d) Red light for dark adaptation e) Thresholds i) Absolute thresholds (1) ~0.000001 mL ii) Ricco’s Law (1) C = A x I iii) Bloch’s Law (1) C = T x I iv) Flicker (1) CFF: critical flicker frequencyPsychology 3041/6014 Spring, 2014 3 of 5 2) Acuity a) Types i) Detection ii) Vernier iii) Resolution iv) Recognition v) Dynamic b) Visual angle i) As an object moves away, it needs to get bigger to maintain the same level of acuity (up to a point) ii) Formula (large angles) iii) Formula (small angles—most vision purposes) iv) Thumb examplePsychology 3041/6014 Spring, 2014 4 of 5 c) Eye charts i) Define: normal = 1 minute of arc is the minimum visual angle for recognition acuity ii) 1 minute = 1/60 of a degree = 0.0167 degree iii) ?? minimum size at 1 meter ?? tan ß = S/D tan 0.167 = S/100 cm 0.00029 = S /100 S = 0.03 cm, or 0.3 mm iv) Note: this is not the size of the letter, but rather the minimum thickness of the lines that make it up. v) Snellen acuity (1) 20/20 defines “normal” (2) 20/200 defines legally blind 3) Eye movements a) Saccades i) See also fixations and regressions b) Pursuit movement c) Vestibulo-ocular movements d) Vergence movements e) Miniature eye movements f) Mixed-modePsychology 3041/6014 Spring, 2014 5 of 5 4) Temporal factors in vision a) Note Bloch’s Law b) Masking i) Forward masking ii) Backward masking iii) Saccadic omission c) After effects i) Brief stimulus ii) Prolonged stimulus iii) Tilt after effect iv) Curvature after effect v) Note: Color after effects discussed next
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