PSYCH 240 1ST Edition Lecture 3 Outline of Last Lecture I. Processes of Perception Outline of Current Lecture I. Overview of VisionII. The EyeIII. Ganglion CellsIV. The ThalamusV. Cerebral CortexVI. Visual CortexVII. Two Visual Pathways: what vs. whereCurrent LectureI. Overviewa. The distal stimulusi. Light is emitted from a light sourceii. Some frequencies of light are absorbed by a distal stimulusiii. Other frequencies of light are reflectediv. Some of this light reaches your eyesII. The eyea. Retinai. The light sensitive cells are at the back, they send signals to the front of the eye (the ganglia cells) which then sends the signal to the brain. It works backwardsii. Rods and cones are photo-receptors. Respond when exposed to lightiii. A photo-chemical reaction takes place inside these cells when exposed to light1. Rods detect brightness2. Cones detect color, they are concentrated in the foveaa. Most people have 3 types of cones: blue, green, rediv. More cones in the fovea where you’re eyes are focusing, more rods in theperipheral (don’t need much color when using your peripheral vision)1. You can actually see better in the dark if you look through your peripheral vision because it has more rodsIII. Ganglion cells (need to understand neurons to understand ganglion cells)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.a. Neurons 1. Dendrites: branches attached to soma2. Soma: cell body – where nucleus is, metabolism, etc. 3. axon – major output center for cellii. Potential: difference in change inside vs outside axon1. Naturally in a depolarized state (-67mv to a +charge)b. Neural Firingi. Threshold: potential must get above threshold level for neuron to fire1. Firing = generating an action potentialii. All-or-none: AP always has same strength. Either you get all of it (if above threshold) or none of itiii. Propagation: once past threshold, active process (ion pumping) propagates action potential down axoniv. Refractory period: short period after firing before neuron can fire againa. Neural Transmissioni. When one neuron fires it can cause neighboring cells to fire (or it can prevent them from doing so)  signal can move from on cell to anotherii. Communicate by sending chemical neurotransmitters (NT’s) across very small gaps btwn cells (synapses)iii. Neural transmission is electrochemical1. Involves an electrical action potential (AP) w/in cells2. Involves a chemical NT btwn cellsi. When NT is released into synapse, it binds to receptors on target neuronii. Causes chain of events that eventually change potential across axon of target cella. Some NT are excitatory (glutamate, etc.)b. Some NT are inhibitory (GABA, etc.)iii. Same thing is happening at 1000’s of other synapses on the target celliv. Summation: if combined effects at all synapses take potential across axonthreshold, then neurons will fire an action potentialb. Mapping the Receptive Field of a Ganglion Celli. When shown light that is not in the circle, the ganglion cell fires at baseline levelii. Firing increases when a light is presented in the circleiii. Other ganglion cells will respond to light in a different circle and will increase firing when a light is pointed at that point. iv. There is typically a donut area around the focus circle that actually inhibits the cell’s firing 1. On-center, off-surrounda) There is a circle that excites the cellb) There is a donut around the circle that inhibits the cellc) There is space around the donut that does nothing and thecell continues to fire at baseline2. Off-center, on-surrounda) Center of circle inhibits, donut around circle excitesv. Center-surround organization1. Functions:a) Point detectionb) Edge detectionc) Light-on-dark or dark-on-lightvi. If one center-off ganglion cell is firing, the brain is going to see it as a single black dotvii. A population of ganglion cells firing can be read by the brain as an edge oreven a dotIV. The Thalamus: your brain’s switchboard operatora. Takes sensory info and sends it to your cortexb. Diff parts of the thalamus handle diff types of infoi. The lateral geniculate nucleus (LGN) handles visual infoMagno “big” Parvo “small”Transient response – only briefly respond to a stimulusSustained response – fire for a long timeLarge receptive field – large sensitive area that will allow cell to fireSmall receptive field – responds to a small area of visual fieldMovement/location Patterns/color/formV. Cerebral Cortexa. Gray matter on the outside of the braini. Frontal lobeii. Parietal lobeiii. Temporal lobeiv. Occipital lobe (visual cortex is here)VI. Visual Cortexa. Rods and cones bipolar cellsganglion cells parvocellular ventral stream (temporal lobe) . magnocellulardorsal stream (parietal lobe)b. Simple Cortical Cellsi. Bar of lightii. Specific orientationiii. Specific retinal positionc. Complex Cortical Cellsi. Edges, movement, orientation, AND location1. Edge detection a. Edges in images correspond to edges of real-life objects (help figure out shape)b. Edges offer depth cuesc. Edges allow parts of 3D objects to be identifiedd. Hyper-complex Cellsi. Very specific shapesii. Comersiii. gapsVII. Two visual pathways: what vs. wherea. Ventral pathway (to remember think: the fin below the shark is ventral because “v” is below “d” in the alphabet)i. “what” something isii. Sax Reading – Dr. P. couldn’t figure out what things wereb. Dorsal Pathway (on top of the shark)i. “where” something isii. McClosky Reading– patient A.H. can’t figure out where things arec. Positron Emission Tomography (PET scans)i. Mental activityneural activityblood flowmore radioactive tracermore positrons emittedii. Get injection of tracer that goes where the blood goes, goes to the most active parts of the brain. This tracer decays and emits positrons that the PET scan can detectiii. Kohler Experiment– spatial vs. object processing1. Spatial (where) task should activate occipital and parietal regionsa. Task: locations – same or different?2. Object (what) task should activate occipital and temporal regionsa. Task: objects – same or different?3. RESULTS: both tasks activate primary visual cortexa. Spatial task tended to activate the dorsal areab. Object task tended to activate ventral area more than spatial taskd. Population Codingi. Is there a