Chapter 5 The Perceiving Mind Sensation and Perception How does Sensation Lead to Perception Sensation the process of detecting environmental stimuli or stimuli arising from the body Sensory systems have developed through natural selection Perception the process of interpreting sensory information Sensory Information Travels to the Brain Sensation begins with interaction between a physical stimulus and our biological sensory systems Stimulus anything that can elicit a reaction from our sensory systems Transduction the translation of incoming sensory information into neural signals The Brain Constructs Perceptions from Sensory Information Attention a narrow focus of consciousness o Often determines which features of the environment influence our subsequent thoughts and behaviors Unfamiliar changing or high intensity stimuli impact our survival and have high priority for our attention Sensory adaptation the tendency to pay less attention to a non changing source of stimulation To prioritize input we use selective attention or the ability to focus on a subset of available information and exclude the rest Bottom up processing perception based on building simple input into more complex perceptions o Simple things o Only need this to respond appropriately to simple stimuli Top down processing a perceptual process in which memory and other cognitive processes are required for interpreting incoming sensory information o Reading a sentence o Recognizing a friend in a crowd Measuring Perception Psychophysics The study of relationships between the physical qualities of stimuli and the subjective responses they produce o Allows us to establish the limits of awareness or thresholds for each of our sensory systems o Developed by Gustav Fechner Absolute threshold the smallest amount of stimulus that can be detected Difference threshold the smallest detectable difference between two stimuli o As stimuli get larger differences must also become larger to be detected Signal Detection Signal detection the analysis of sensory and decision making processes in the detection of faint uncertain stimuli o Two step process 1 the actual intensity of the stimulus which will influence the observer s belief that the stimulus did occur 2 the individual observer s criteria for deciding whether the stimulus occurred How Do We See Vision the sense that allows us to process reflected light 50 of our cerebral cortex processes visual information Visual Stimulus visible light is a type of radiation emitted by the sun other stars and artificial sources such as the lightbulb energy moves in waves Wavelength is decoded by our visual system as color or shaes of grey The height of the waves is translated by the visual system into brightness The Biology of Vision The eye o Hard outer covering helps the fluid filled ball retain shape o Cornea the clear surface at the front of the eye that begins the process of directing light to the retina o Pupil an opening formed by the iris o Iris the brightly colored circular muscle surrounding the pupil of the eye Adjusts the opening of the pupil in response to the amount of light present and to signals from the autonomic nervous system Arousal dilated pupils Relaxation constricted pupils o Lens the clear structure behind the pupil that bends light toward the retina Muscles attathed to the lens can change its shape allowing us to adjust our focus to see near or distant objects o Retina layers of visual processing cells in the back of the eye A thin but complex network of neurons specialized for the processing of light In the deepest layer of the retina are specialized receptors called rods and cones that transduce the light info Before light reaches these receptors it must pass through numberous blood vessels and neural layers We do not see the vessels and neural layers due to adaptation Sensory systems tune out stimuli that never change o Optic disk where blood vessels leave the retina to form the optic nerve exit Because there are no rods or cones in here the eye has a blind spot o Fovea an area of the retina that is specialized for highly detailed vision Responsible for central vision as opposed to peripheral vision o The image projected on the retina is upside down and reversed relaive to the actual orientation fo the object being viewed Rods and Cones Rod a photoreceptor specialized to detect dim light o More sensitive to light o More common as you move from the fovea to the periphery of retina o Do not provide info about color o Not clear sharp images Cone a photoreceptor in the retina that processes color o Excel at seeing dim light o Function best under bright light o See sharp images and color Human eye contains about 120 million rods and 6 million cones Visual Pathways Rods and cones are the only true receptors of the visual system They trigger responses in four additional layers of neurons within retina Optic nerve the nerve exiting the retina of the eye Chiasm the point at which the optic nerves cross the midline Optic tracts nerve pathways traveling from the optic chiasm to the thalamus The thalamus sends info about vision to the amygdala and primary visual cortex in hypothalamus and midbrain occipital lobe Primary visual cortex responds to shape location movement and color Parietal pathway process movement in the visual environment Temporal pathway responds to shape and color and contributes to our ability to recognize objects and faces Visual Perception and Cognition Color Vision Red green and blue are primary colors Trichromacy theory a theory of color vision based on the existence of different types of cones for the detection of short medium and long wavelength o One or no cones see just black white and grey o Two cones are color blind o Three cones normal Opponent process theory a theory of color vision that suggests we have a red green color channel and a blue yellow color channel in which activation of one color in each air inhibits the other o We cannot see a color like reddish green or bluish yellow because they share the same channel Recognizing Objects Feature detector a hypothetical cell that responds to only one specific visual stimulus The visual system may perform a mathematical analysis of the visual field While the hierarchical model implies a reality built out of indivudial bars and edges the mathematical approach suggest that we analyze patterns of lines o Simplest gratings o Gratings vary in two dimentions frequency and contrast Gestalt Psychology