Sensory Thresholds and Signal Detection Qualities of Sensation Boring (1953) • Modality-Specific – Vision: Hue, Saturation – Audition: Pitch, Timbre – Olfaction: Odor – Gustation: Flavor – Touch: Roughness, Wetness – Pain: Sensory Pain (Fast/Slow), Suffering • General: Intensity – Vision: Brightness – Audition: Loudness Thresholds for Conscious Awareness • Absolute – Weakest Detectable Stimulus • Relative – Smallest Detectable Change • “Just-Noticeable Difference” – Absolute Threshold a Special Case • Isomorphism – Physical Intensity – Sensory Intensity Neural Coding of Intensity The “All or None” Law Weber’s Law Weber (1846) Change in Intensity (dI) dI/I = c Original Intensity Noticeable Change 10 11 100 110 200 220 25 20 15 10 5 0 10 100 200 Original Intensity (I) c = 1/10 Representative Weber Fractions for Human Sensation Geldard (1962) Modality Visual Brightness (White) Lifted Weight Thermal Pain Auditory Loudness Cutaneous Pressure Smell of Rubber Taste of Salt c 1/60 1/50 1/30 1/10 1/7 1/4 1/3 Fechner’s Law Fechner (1860) S = klogI 10 Sensory Intensity 0 1 2.5 Intensity of Sensation (S) Physical Intensity 1 2.3 2 1.5 1 2 200 2.3 1 0.5 0 -20 100 2 0 0 20 40 60 80 100 120 140 160 180 200 Intensity of Stimulus (I) k = 1, log = log10 Fechner’s Law as Logarithm Fechner (1868) S = klogI Intensity of Sensation (S) 3 3 2.5 2.3 2 2 1.5 1 1 0.5 0 0.1 0 10 Intensity of Stimulus (I) 1000 Physical Intensity 1 10 100 200 1000 Sensory Intensity 0 1 2 2.3 3 Fechner’s Law Fechner (1868) S = klogI • Sensation Grows More Slowly Than Stimulation – Sensory Receptors Compress Stimuli • Exceptions – Perceived Length – Perceived Pain Stevens’ Law Stevens (1961) S = kIN Fechner’s Law Intensity of Sensation (S) 15 14.14 10 10 5 3.16 Sensory Intensity 1 10 3.16 100 10 200 14.14 1 0 -20 Physical Intensity 1 0 20 40 60 80 100 120 140 160 180 200 Intensity of Stimulus (I) k = 1, N = 1/2 Stevens’ Law Stevens (1961) S = kIN Intensity of Sensation (S) The Case of Length 200 175 150 125 100 75 50 25 10 1 0 -20 -25 0 20 40 200 100 60 80 100 120 140 160 180 200 Intensity of Stimulus (I) k = 1, N = 1 Physical Intensity 1 Sensory Intensity 1 10 10 100 100 200 200 Stevens’ Law Stevens (1961) S = kIN The Case of Pain Intensity of Sensation (S) 3000 2828 2500 2000 Physical Intensity 1 Sensory Intensity 1 10 31.6 100 1000 200 2828 1500 1000 1000 500 0 -20 0 1 31.6 20 40 60 80 100 120 140 160 180 200 Intensity of Stimulus (I) k = 1, N = 3/2 Stevens’ Law Stevens (1961) • A General Psychophysical Law: S = kIn • Operating Characteristic of Receptors – Most Compress Stimulation: n < 1 – Some Expand Stimulation: n > 1 Representative Exponents (n) Viscosity of silicone Fluid: 042 Brightness of Point Source: 0.5 Loudness of Pure Tone: 0.67 Area of Square 0.70 Length of Line: 1.00 Pressure on Palm: 1.10 Taste of Saccharin: 0.8 Taste of Sucrose: 1.3 Heaviness of Lifted Weight: 1.45 Electric Shock to Fingers: 3.50