Sensation & Perception

Sensation & Perception

1. Psychophysics: Basic Concepts and Issues

   • Psychophysics: The study of how physical stimuli are translated into psychological experience
   • Thresholds: A dividing point between energy levels that do and do not have a detectable effect
     • Absolute Threshold: For a specific type of sensory input is the minimum amount of stimulation that an organism can detect
     • JND: The smallest difference in the amount of stimulation that a specific sense can detect
       • Weber's Law: States that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus
   • Signal Detection Theory: Proposes that the detection of stimuli involves decision processes as well as sensory processes, which are both influenced by a variety of factors besides stimulus intensity.
     • Hits: Detecting signals when they are present
     • Misses: Failing to detect signals when they are present
     • False Alarms: Detecting signals when they are not present
     • Correct Rejections: Not detecting signals when they are absent
     • Detectability: Measured in terms of probability and depends on decision-making processes as well as sensory processes
   • Subliminal Perception: The registration of sensory input without conscious awareness
   • Sensory Adaption: A gradual decline in sensitivity due to prolonged stimulation

2. Our Sense of Sight: The Visual System

   • The Stimulus: Light
     • We need light to see
     • Light waves vary in amplitude (height) and wavelength (distance between peaks)
     • Measured in Purity: How varied the mix is
     • Ultraviolet = shorter wavelengths
     • Infrared = longer wavelengths
   • The Eye: A living Optical Instrument
     • Two main purposes
       • 1. Channel light to the neural tissue that receives it (retina)
       • 2. Houses the Retina
     • Lens: Transparent eye structure that focuses the light rays falling on the retina
       • Accommodation: When the curvature of the lens adjusts to alter visual focus. Closer = Fatter (rounder) and Distant = flatter
     • Nearsightedness: Close objects are seen clearly but close distant objects appear blurry
     • Farsightedness: Distant objects are seen clearly but close objects appear blurry
     • Pupil: The opening in the centre of the iris that helps regulate the amount of light passing into the rear chamber of the eye
     • Our eyes are in constant motion called Saccades and are important so we don't experience sensory adaption and lose sight of things around us
   • The Retina: The Brain's Envoy in the Eye
     • The neural tissue lining the inside back surface of the eye; it absorbs light, processes images, and sends visual information to the brain
     • Processes images
     • Optic Disk: a hole in the retina where the optic nerve fibres exit the eye
     • Two kinds of visual receptors located in the innermost layer of the retina
       • Cones: Specialized visual receptors that play a key role in daylight vision and colour vision
         • Visual Acuity: Sharpness and precise detail
         • Fovea: A tiny spot in the centre of the retina that contains only cones; visual acuity is greatest at this spot
       • Rods: Specialized visual receptors that play a key role in night vision and peripheral vision
     • Dark Adaption: The process in which the eyes become more sensitive to light in low illumination
     • Light Adaption: The process whereby the eyes become less sensitive to light in high illumination
     • Optic Nerve: A collections of axons that connect the eye with the brain
     • The Receptive Field: The Retinal area that when stimulated affects the firing of that cell
   • Visual Pathways to the Brain
     • Optic Chiasm: The point at which the optic nerves from the inside half of each eye cross over and then project to the opposite hald of the brain
     • LGN: Lateral Geniculate Nucleus where 90 percent of the axons from the retinas synapses are located and visual signals are processed.
   • Viewing the World in Colour
     • Subtractive Colour Mixing: Works by removing some wavelengths of light, leaving less light than was originally there
     • Additive Colour Mixing: Works by superimposing lights, putting more light in the mixture than exists in any one light by itself
     • Trichromatic Theory: Colour vision holds that the human eye has three types of receptors with differing sensitivities to different light wavelengths
     • Colour-blindness: Encompasses a variety of deficiencies in the ability to distinguish among colours
     • Complementary Colours: Pairs of colours that produce grey tones when mixed together
     • Afterimage: A visual image that persists after a stimulus is removed
     • Opponent Process Theory: Holds that colour perception depends on receptors that make antagonistic responses to three pairs of colours
   • Vison and the Brain
     • Feature detectors: Neurons that respond selectively to very specific features of more complex stimuli
     • visual agnosia: An inability to reorganize objects
     • Prosopagnosia: An inability to recognize familiar faces

3. Our Sense of Hearing: The Auditory System

   • Cochlea: Fluid-filled, coiled tunnel that contains the receptors for hearing
   • Basilar Membrane: Runs the length of the spiralled cochlea, holds the auditory receptors
   • Theories of Hearing
     • Place Theory: Holds that perception of pitch corresponds to the vibration of different portions, or places, along the basilar membrane
     • Frequency Theory: Holds that perception of pitch corresponds to the rate, or frequency, at which the entire basilar membrane vibrates