to Introduction Sensation and Perception Overview of Today: Discuss Basic Processes of Sensation and Perception Review Visual Processes in Detail, with figures and videoclips Examine How Perception is "Constructed" and what features influence the construction process Basic Processes of Sensation 1) Modification via accessory structures energy input and operating on it to make sense of it. 2) Transduction 3) Encoding 4) Representation in Cortex
Modification of Stimuli via Accessory Structures e.g., lens of eye is accessory structure that changes light by focusing it outer part of ear is accessory structure that collects sound
Detectable Energy is Transduced Transduction is a chemical process of converting energy into neural activity or code Transduction Occurs at Sensory Receptors, which are cells that specialize in detecting certain forms of energy (light waves, sound waves, heat, etc.) Sensory Receptors respond especially to CHANGES in stimulus intensity Adaptation (decreased responsiveness in firing of cells and concomitant conscious experiencing) occurs to an unchanging stimulus over time Transduction results in encoding of energy that is detected/sensed:
Coding is the translation of physical stimulus properties into patterns of neural activity that specifically identify those physical properties Final output is action potentials firing down sensory neurons The rates of firing of coalitions of action potentials "represent" "re-presentation" of sensation at the level of brain activity the external stimulus in the final stage of sensation. Encoded Information is "Represented" in Cortex Thalamus is Relay Station for Sensory Information (except smell) Cortical Representations are Topographically Contralateral to part of world sensed opposite side of brain uses opposite side of body for stimuli and use Topographical Representations exist in cortex 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 fovea in the middle of the eyeball contain cones that receive light and allow us to see color. Note the image in the book Visual Sensation The Main Pathway From the Distal Stimulus to the Proximal Stimulus: How Sensory Information Arrives in Visual Areas of Occipital Lobe
Distal Stimulus-----> observing something occurring, the actual object that you are viewing.
Proximal Stimulus ----> The thing that we come to know. The image that comes through the eye, a series of processes that go through the brain allowing us to register the distal stimulus
A closer look at the eyeball and some of its important structures: modification structures: cornea, iris, pupil allows light to come through the eyeball, adjusts size to let in more or less light, lens inverts the image.
photo receptive layer- rods and cones. rods let us see and discern objects when it's darker, tend to be found on the edges of the photo receptive layer. Cones are numerous and dense towards the center, where the most light is,
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 Feature Detectors are neurons "specialized" to fire only in response to select dimensions of light stimuli. Very particular stimuli cause this response. These critical are to the ultimate perception of visual objects.
Videoclip: 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 different cells react to different properties simple cells respond only to specific angles of light information
complex cells take information from multiple simple cells and integrate them into the brain hypercomplex cells take information from multiple complex cells and piece it together to find the whole picture from total stimulus Perceptual Processes: Beyond Sensation Perception involves "Construction" of the World Construction involves: selection of sensory input: what to pay attention to organization of sensory input: interpretation of sensory input: what is it? Perceptual Construction is influenced by attitudes, preferences, and social-situational contexts of perception (i.e., expectations) Simple Example: Context Effects
We experience everything in context. 12 A 13 C 14 Gestallt psychology, the whole is greater than the sum of its parts. Closure in open or ambiguous figures. Fill in the gaps of broken pictures.
Videoclips of Context Effects and Role of Personal Factors:
Discussion of Sack's Cases Dr. P and the hat- he doesn't see images as a whole. He can only distinguish family members by specific points and features of their bodies. Used music to focus and organize himself.Could only do things like eating and dressing in a specific routine and pattern. Only describes things seen on the right when asked to take an imaginary walk through the square.His left hemisphere seems to be intact based on this. Left hemisphere specializes in language and elements. Right hemisphere
specializes in wholes and faces. Occipital and Propriatal lobe seem to be disturbed. Problem of perception, not sensation. He can see things, he just doesn't know what they are because his perception is so messed up, ie wife's head is hat, fire hydrant is dog. Jimmy the Lost Mariner Christian the Disembodied Woman- She couldn't control her body muscles and facial muscles. Her proprioception was off and she couldn't control her body stance. She was blind to her body. Sensory neuritis- something very wrong with sensory nerves that allow her to not feel her body. Most likely caused by her antibiotics given to Christina before her surgery. She had to learn how to visually do everything, and watch herself move things, walk and eat in order to accomplish anything. Ray Witty-Ticcy- The drummer who likes to swear all the time. Terretts disorder. Given an antipsychotic drug to decrease dopamine by blocking post synaptic receptors. Drugs seemed to effect his drumming, which upset him. Natasha Cupid- She had syphilis. Given drugs to stop spread of infection. Symptom was that she was feeling a little frisky... she's a rather old woman and so her friends are distressed, hence the reason she sees the doctor Madeline hands- Has hands that are useless God forsaken lumps of dough. Her senses are intact. But has never really used her hands because everyone always did things for her. She needed to be taught how to use her hands, feed herself, write, hold on to things. Eventually she loves using her hands and sculpts. Mr. McGregor- Had Parkinson's disease, destruction of dopamine neurons in Basal Ganglia. He walks at a tilt and he can't see it so they make him look into a mirror and watch tapes. So he constructs 'level glasses' like a carpenters level in order to see himself tipping and fix the problems. Stephen the Dog- his olfactory senses are dis-inhibited probably because of dopamine excess from using Cocaine. Smells everything.