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Chapter 3

Chapter 3.docx

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Blaine Mullins

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Chapter 3­ Perception - Case Study: Unusual perceptual experiences » Visual agnosia: can’t identify objects visually but can identify them using other senses (ex. touch) damage to temporal lobe » Blindsight: damage in visual cortex leads to inability to see anything in a certain part of the visual field  can still accurately make judgments about objects in blind pot (not consciously aware)  Why do we need consciousness if we can still see subconsciously  2 pathways: visual cortex and brainstem pathway to brainstem is older and remains intact during Blindsight (unconscious)  Like we have two brains » Optic ataxia: can’t reach for an object (but can identify it) - Sensation: activation of sensory organs by stimulus » Transduction: conversion of physical stimulus (light or mechanical) into neural impulses » Sensory organs: hair cells (hearing), rods/cones (vision), mechanoreceptors (touch), A-beta & C fibers (pain), taste cells - Perception: processing sensory info. in a way that produces conscious awareness and guides action in the world » We have perception to know what and where things are use properties such as brightness, colour, shape, size to interact with objects » Perceptual system is constantly changing » Receive info. from the environment nervous system/brain processes info. use knowledge, expectations to find out how to interact with the object » Automatic, fast and requires little resources Problems with Perception - What we see, hear is an illusion - McGurk effect: we experience different levels of pain depending on the intention if someone intentionally causes you pain, it feels more painful than if it was an accident - Light indeterminacy: we don’t know how much light the actual object is reflecting affected by light source, shadows, reflectance » Luminance: amount of light that enters from eye - Shape indeterminacy: many 3D shapes have the same 2D shape (ex. cube/square-based pyramid can both have a square 2D shape) » Some objects are partially hidden » Three lines that intersect can be seen as coming towards or away from you - Size indeterminacy: if an object is small, it is small in size or it is far away - Solutions: » Use likelihood it is more likely that the object is not at a weird angle » Use frame of reference to judge shape of object » Distinguish shadows from different objects because shadows have fuzzy edges and move with the object » Convergence: adjust lens to see far away or close objects » Retinal disparity: 2 eyes have slightly different image on retina can use this to judge see depth » Familiar size: use surrounding objects if object is too big, it is probably photo shopped Perception and Awareness - People aren’t consciously aware of all objects in their environment (two different travelers visiting the same place will remember different things) - Encoding: transforming info. into other forms of representation » Automatic, fast, and unconscious the process is too complex for us to be aware of everything all the time » Multidimensional encoding: info. can be encoded across dimensions (ex. vision, hearing, emotion) - Subliminal perception: can affect behaviour but happens too fast for someone to be consciously aware of it » Limen: threshold for being aware of a stimulus  Subliminal: below threshold » Problem: we have no way of knowing the person wasn’t actually aware of it - Backward masking: present a target stimulus and then quickly present another stimulus/mask » Used because we have iconic memory once we see something for a brief second, our brain holds the image for a few more seconds » If another stimulus is presented right after, the visual system is distracted and won’t hold the image anymore - Stimulus onset asynchrony (SOA): delay between first stimulus and target stimulus - Priming: tendency for initial stimulus to make subsequent response to related stimuli more likely (ex. show word and then a pattern people were more likely to pick words from a list similar to the first word presented) » Direct measure: participants report they have seen the stimulus » Indirect measure: effect of undetected stimulus is determined on a subsequent task - Objective threshold: point where participants can detect the stimulus 50% of the time (chance level) - Subjective threshold: point where participant tells you they don’t observe the stimulus anymore - Process dissociation procedure: requires participants not to respond if they have seen the item previously » If they were aware of the item, they would not respond the second time The Visual System - Half of the brain does visual processing not just the striate cortex - Each eye receives input from right and left visual field - Temporal retina: close to temples (outer part of eye) » Ipsilateral light that hits here goes to same side hemisphere - Nasal retina: close to nose (inner part of eye) » Contralateral  light that hits here goes to opposite hemisphere - On-center/off-center cells: activate when stimulus hits the middle and inhibit when stimulus hits outer area - Lateral inhibition: activation of one neuron inhibits those around it - Visual Pathway: eye optic nerve optic chiasm lateral geniculate nuclei/superior colliculus optic radiation primary visual cortex (V1) - Dorsal Pathway: involved in motion, spatial information (where pathway) » Goes to parietal lobe » Landmark discrimination problem: a marker is next to a door choosing that door = food » Damage to dorsal stream = can’t locate landmark - Ventral Pathway: involved in identification of object like detail, shape, colour, size (what pathway) » Goes to temporal lobe » Object discrimination problem: choose certain object choosing right object = food » Damage to ventral stream = can’t identify objects - What/Where Pathways: the what pathway is tied in with the where pathway (in order to know where something is, you need to know what it is) Ungerleider/Mishkin - What/How Pathway: dorsal pathway gives up spatial information and allows to move and interact with object  Goodale and Milner » Temporal lobe is activated during identification of object and parietal lobe is activated when grabbing something » Ex. steepness of hills, we overestimate steepness of hill but we can predict the slope accurately using a board Weird Stuff - Mirror neurons: neuron that fires when an animal performs an action AND when he/she observes another monkey or human performing the same action (don’t activate when using pliers to pick up objects) - Allows us to understand other people’s behaviour, intentions, empathy, self-awareness - Synesthesia: condition where activation of one sense activates another sense simultaneously sensory problem (no cognition) » Most common form is seeing colour in numbers » Clinical test: show bunch of letters and ask person to find a shape synesthetic person can find it fas
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