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Understanding the Visual Sensory Systems: Light Stimuli, Receptor Processes, and Perception

This overview delves into the visual sensory systems, focusing on the nature of light as electromagnetic energy and the characteristics of visual stimuli, including hue, saturation, and brightness. It explains the structure of the eye and the role of rods and cones in vision, along with processes for depth perception and visual search. Key concepts in bottom-up versus top-down processing and factors influencing detection and response bias in visual tasks are also discussed. This comprehensive analysis is crucial for understanding human visual perception.

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Understanding the Visual Sensory Systems: Light Stimuli, Receptor Processes, and Perception

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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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