Psych 202 1st Edition Lecture 18 Introduction to Sensation and Perception Overview of Today Discuss Basic Processes of Sensation and Perception Review Visual Processes in Detail with figures and video clips Examine How Perception is Constructed and what features influence the construction process Basic Processes of Sensation 1 Modification of stimuli via accessory structures o e g lens of eye is accessory structure that changes light by focusing it o outer part of ear is accessory structure that collects sound 2 Transduction o Detectable Energy is Transduced o Transduction is process of converting energy into neural activity o Transduction Occurs at Sensory Receptors which are cells that specialize in detecting certain forms of energy light waves sound waves heat etc o Sensory Receptors respond especially to CHANGES in stimulus intensity o Adaptation decreased responsiveness in firing of cells and concomitant conscious experiencing occurs to an unchanging stimulus over time 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 3 Encoding o Transduction results in encoding of energy that is detected sensed o Coding is the translation of physical stimulus properties into patterns of neural activity that specifically identify those physical properties o Begin with the action potentials sent by the ganglion cells 4 Representation in Cortex o Final output is action potentials firing down sensory neurons o The rates of firing of coalitions of action potentials represent the external stimulus in the final stage of sensation o Encoded Information is Represented in Cortex o Thalamus is Relay Station for Sensory Information except smell Cortical Representations are Topographically Contralateral to part of world sensed left and right Topographical Representations exist in cortex o e g somatosensory cortex visual cortex auditory cortex etc Example Recall the split brain video and how visual information was presented and then cortically represented Next slides demonstrate the process Visual Sensation begins with the modification structures in the eyeball Cornea iris pupil lens Retina photo receptor area has 2 different types of cells rods and cones o Rods respond to dark lower levels of illumination distributed to retina more o Cones respond to light more centrally located The Main Pathway From the Distal Stimulus to the Proximal Stimulus How Sensory Information Arrives in Visual Areas of Occipital Lobe Distal stimulus stimulus that is outside what you re looking at when you watch someone do something what you are looking at Proximal stimulus on the retina and brain inside in your body we know this process A closer look at the eyeball and some of its important structures A closer look at transduction and encoding structures Transduction structures the photoreceptive layer note the distribution of rods and cones relation to fovea Encoding structures output from bipolar cells creates coding in ganglion cells which collectively form the optic nerve and relay ultimately to the occipital lobe From Visual Sensation to Visual Perception the role of feature detectors Modification structures cornea iris pupil lens Feature Detectors are neurons specialized to fire only in response to select dimensions of light stimuli o These are critical to the ultimate perception of visual objects o Work with other processes to build a perception of what is actually happening Video clip Feature Detectors in Visual Sensation Hubel and Weisel 1981 received Nobel Prize for their identification and specification of feature detectors in visual cortex of cats o Simple cells o Complex cells o Hypercomplex cells Perception involves construction of the world o Construction involves top down process what we expect to see alters what we are actually seeing processes involved in of construction of perceptual world from sensory input Selection of sensory input your brain has to decide what to pay attention to what to notice Organization of sensory input Interpretation of sensory input Perceptual Construction is influenced by attitudes preferences and socialsituational contexts of perception i e expectations bottom up Simple Example Context Effects Gestalt principles of perception o Make hypercomplex cells Perceptual Processes Beyond Sensation Make complex cells Closure continuity Video clips of Context Effects and Role of Personal Factors One image see two different things o Old woman vs young woman Discussion of Sack s Cases Hands Madeline Witty Ticcy Ray Cupid s Disease Natasha The Man Who Mistook His Wife for a Hat Dr P The Disembodied Lady Christina On the Level Mr McGregor The Dog Beneath the Skin Steven