Chapter 2 Other Ways of Seeing the World Vision Evolution of Eyes o Vertebrates Animals with backbones have rods for achromatic black white vision vs cones for chromatic vision o Vertebrates and octopus octupus has nerve fibers BEHIND rods and cones vs humans with the nerve fibers on top of rods and cones Vertebrate Eye Adaptations o Diurnal Vertebrates active during the day Human and pigeon Mostly cones in fovea Sharp vision at expense of light sensitivity o Nocturnal vertebrates active at night Mouse and owl Light sensitivity at expense of sharp vision rely on other senses such as hearing Mostly rods in fovea o Arrhythmic vertebrates equally active day and night Dog Must have both sharp and light sensitive vision Have both rods and cones in the fovea Evolution of visual pigments o Visual pigments in human vision 4 visual pigments in human retina Rhodopsin Blue green and red pigments in 3 different types of in rods cones o Visual pigments Differ in sensitivity to different wavelengths of light Molecules embedded in outer cell membrane of rods and cones Light activates pigment which causes a change in signal sent to o Distribution of Rod Rhodo sin peak sensitivity for several 100 species Visual pigments differ among species in poin of peak nervous system sensitivity to light Rhodopsin pigment found in rods that is responsible for black white vision varies in sensitivity across species o Evolution of Color Vision Pigments African cichlid fish of the East o Evolution of Visual Pigments in the Cottoid Fish Species of Lake African Rift Lakes Baiakal Russia Lake Baikal is the deepest and oldest lake in the world 25 30 million years old As much water as the great lakes combined Animal Psychophysics Known as Galapagos of Russia because its isolation and age have given it world s richest and most unusual freshwater fauna Over 50 of the species are unique to the lake Coloration of animal gets less and less the deeper in the lake Coloration necessary for mating Animals rhodopsin and color pigments adapt through lower you go depth o Psychophysics field of perception that attempts to measure or quantify sensitivity of perceptual systems to different dimensions of physical stimulation Determination of sensory thresholds o Originated by German physicist Gustav Fechner o Absolute threshold By raising and lowering stimulus intensity we can determine Absolute threshold point at which a stimulus is detectable the minimum energy a sensory system can detect 50 of the time Titration method detectable then raise it until it is then lower and raise it again Average of the switches is the absolute threshold lower intensity until stimulus is not o Dark adaptation function in humans For about the 1st 10 minutes in the dark the cones require less light to reach a threshold response than do the rods therefore the rods require less light Point at which rods become more sensitive is called the rod cone break o Blough s Pigeon titration method Pigeons were trained to peck key A vs key B when they saw the stimulus vs when they did not Trained to peck key A when light was on and key B when it was off on partial reinforcement schedule Dark adaptation curves in pigeons Psychological methods originally developed for humans can be adapted for use with animals o Spectral sensitivity in pigeons Blough was 1st to characterize spectral sensitivity in animals by using his titration procedure for pigeons Blough s studies showed that animals have sensory systems that work like ours do Spectral sensitivity wavelengths of light differential sensitivity to different Pigeons are more sensitive to ultraviolet and less sensitive to red than we are o Pattern perception Nobel prize winners David Hubel and Torsten Wiesel discovered feature detectors groups of neurons in visual cortex that respond to different types of visual stimuli o Basic features color luminance flicker polarity Bottom up perception orientation etc Physical characteristics of stimuli drive perception Realism Low level information can be extracted from sensory information using neural feature detectors we simply sense the world Known neural feature detectors o Brightness color curvature oriented line Gestalt Psychology Kohler and top down perception Human perception is hollistic world is made up of objects against a background Grouping figure vs ground Good configuration points in a line appear as part of a line objects Closure enclosed structures appear to be or imply Top down perception o Knowledge expectations or thoughts influence perception o Constructivism we structure the world Anne Treisman s Feature Integration theory Objects are automatically and preattentively analyzed into features then are combined into coherent perceptual objects during a focused attention stage Processing is different for visual features vs objects involving conjunctions of features o Pop out effects Efficient vs inefficient search Cook s pop out studies in pigeons o Robert Cook o Pigeons pecked at touch screen for grain o Reinforced for pecking letter P Texture Discriminations o Studies using texture stimuli have found the human visual system can quickly group similar color and shape features into global spatial region then rapidly segregate them