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4. Visual Sensory Systems

4. Visual Sensory Systems. THE STIMULUS: LIGHT the visual stimuli as a wave of electromagnetic energy ( fig 4.1a ) visible range of wavelength from 400nm (blue-violet) to 700 nm (red) a given light stimulus characterized by hue, saturation, brightness

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4. Visual Sensory Systems

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  1. 4. Visual Sensory Systems THE STIMULUS: LIGHT • the visual stimuli as a wave of electromagnetic energy (fig 4.1a) • visible range of wavelength from 400nm (blue-violet) to 700 nm (red) • a given light stimulus characterized by hue, saturation, brightness • the source of light by luminous intensity/flux (candela) • illumination – the lighting quality of a given working environment (fig 4.2) • illuminance (照度), luminance (輝度) • Reflectance(%) = luminance (FL) / illuminance (FC) THE RECEPTOR SYSTEM • schematic view of the eyeball (fig 4.3) The Lens • corona  pupil  lens (accommodation)  retina • myopia (근시), presbyopia(노안)

  2. The VisualReceptorSystem • the image may be characterized by its intensity (luminance), wavelengths, and size (visual angle) • VA = 5.7 * 60* (H/D) • two types of receptor cells (rods and cones) • location – cones for fovea (2°of VA) and rods for periphery • acuity – motion in the periphery • sensitivity – advantage of rods in sensitivity • color sensitivity – rods are color blind • adaptation – temporary blindness, glare • differential wavelength sensitivity – cones are generally sensitive to all wavelengths while rods are insensitive long lengths

  3. BOTTOM-UP VS. TOP-DOWN PROCESSING

  4. DEPTH PERCEPTION • depth cues (fig 4.7) • accommodation, binocular convergence, binocular disparity – inherent in the physiological structure (bottom-up processing)  only effective for judging distance, slant, and speed for objects within a few meters • linear perspective, relative size, interposition, light and shading, textual gradients (density) – based on experience (top-down processing) • motion parallax VISUAL SEARCHAND DETECTION Eye Movements • pursuit movement – constantvelocity to follow targets • saccadic movements – abrupt and discrete movements: initiation latency, movement time, destination [dwell: duration (information content, ease of information extraction) and UFOV (foveal region, 2 degrees of VA)] Where’s Wally?

  5. Visual Search The serial Search Model • T= NT/2 • typical search pattern – top to bottom, left to right • random (non-exhaustive) search Conspicuity • bottom-up influence • parallel processing Expectancies • top down processing – based on prior knowledge (experience)

  6. Detection Signal Detection Theory

  7. Sensitivity and Response Bias • sensitivity (d’) – how good an operator is at discriminating the signal from the noise • response bias (response criterion, beta) – expectancy, payoff • ROC (receiver operating characteristic) curve Interventions • A C: instructions, incentives • A B: training, visual template higher sensitivity conservative

  8. brightness hue

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