PSYC 1315 1st Edition Lecture 8 Outline of Last Lecture I Brain size and structure II Endocrine system III Brain damage plasticity and repair IV Genetics and behavior V Health and wellness Outline of Current Lecture I Basic Principles II Visual System Current Lecture I Basic Principles a Sensation the process of receiving stimulus energies from the external environment b Perception the process of organizing and interpreting sensory information c Sensory and Perception i Bottom Up Processing 1 initiated by sensory input 2 outside world s influence on perception ii Top Down Processing 1 initiated by cognitive processing 2 internal mental world s influence on perception 3 expectations prior understanding iii Unified Information Processing System d Sensory Receptors i Photoreceptors ii Mechanoreceptors iii Chemoreceptors These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II e Stimulus Coding i Reception absorb physical energy by receptors ii Transduction conversion of physical energy to an electrochemical pattern in neurons Affects receptor potentials iii Coding one to one communication between an aspect of a physical stimulus and an aspect of neural activity iv Conscious awareness f Sensory Thresholds i Absolute threshold The minimum amount of physical energy needed for an observer to notice a stimulus ii Signal detection theory States that experiencing a sensation means making a judgement about whether a stimulus is present or absent iii Just noticeable difference noticing when a change has occurred in an existing sensation iv Weber s Law two stimuli must differ by a constant minimum percentage not a constant amount to be perceived as different Visual system a Anatomy of the Eye i Pupil an opening in the center of the iris in which light enters the eye ii Retina rear surface of the eye which is lined with visual receptors iii Light from the left side or below of the world strikes the right or top half of the retina and vice versa iv Macula portion of the retina with the greatest ability to resolve detail v Fovea Central portion of the macula specialized for acute detailed vision in humans The blood vessels and ganglion cells are almost absent Little convergence or no convergence between receptors and their postsynaptic cells known as bipolar cells vi The peripheral regions a greater number of receptors for each bipolar cells cannot discern fine detail greater sensitivity to dim light b Route Within the Retina i Within retina light photoreceptors bipolar cells ganglion cells ii Ganglion cell axons optic nerve brain iii Blind spot the point at which the optic nerve leaves the eye because no visual receptors c Visual Receptors i Photoreceptors contain photopigments 1 Rods abundant in the peripheral retina 120 million per retina Involved in both peripheral and night vision 2 Cones found primarily in the fovea 6 million per retina Involved in both visual acuity and color vision d Characteristics of the Visual Cortex i Cells in the visual cortex are grouped together in columns perpendicular to the surface of brain Cells have similar properties ii Cells in the visual cortex have feature detectors which refers to specific neurons responding to specific features e Depth Perception is the ability to perceive objects three dimensionally i Through the use of 1 Binocular input receives input from both eyes 2 Convergence allow us to detect depth and distance 3 Monocular input f Properties of Light i Wavelength distance between peaks 1 perceived as hue 2 some wavelengths beyond human sensation ii Amplitude height of wave 1 perceived as brightness iii Purity mixture of wavelengths 1 perceived as saturation g Color Vision i Human Visual Field Ranges in wavelengths between 350 nm Violet and 700 nm Red ii Trichromatic Theory 1 Thomas Young Herman von Helmholtz 1930s 2 Trichromatic Theory We perceive color through the combination of three kinds of cones each kind maximally sensitive to a different set of wavelengths a Short wavelengths blue b Medium wavelengths green c Long wavelengths red 3 Opponent Process Theory Color is perceived in terms of paired opposites white black red green yellow blue 4 Negative afterimages Result from fatiguing a response by opponent process cells red becomes green green becomes red yellow becomes blue etc 5 Color Constancy The ability to recognize the color of objects despite changes in lighting a Note This ability is not explained by the trichromatic theory or the opponent process theory iii Color Vision Deficiency color blindness the inability to perceive any color rare 1 Most common red green color blindness Due to lack of cones caused by gene deficiency on the X chromosome