Lecture Slides: Visual Perception. Cognitive Psychology PDF

Lecture 4: Visual Perception Cognitive Psychology 2135  Metaphors for the mind The "brain as computer" metaphor. - In this metaphor, the brain is viewed as the hardware, whereas cognitive operations are viewed as software (programs) - The metaphor describes the...

Lecture 4: Visual Perception Cognitive Psychology 2135  Metaphors for the mind The "brain as computer" metaphor. - In this metaphor, the brain is viewed as the hardware, whereas cognitive operations are viewed as software (programs) - The metaphor describes the relationship between brain functions and structure  Metaphors for the mind The “hydraulic metaphor”. - René Descartes (1600's) advocated a model of brain function whereby basic neural functions were governed by a series of tubes carrying “spirits” or vital fluids - Bodily fluids were one of the most obvious indicators of health, sickness, and being alive - Blood, discharge, urine, pus, bile, and other fluids are all indicators of things either working well or not working well and when they stop, we stop  Metaphors for the mind The “hydraulic metaphor” lives on in our language in the conceptual metaphors we use to talk about the brain and mind. - We often talk about cognition and thinking as information “flowing” in the same way that fluid might flow - Common expressions: - “stream of consciousness” - “waves of anxiety” - “deep thinking” - ideas “come to the surface” - memories that come “flooding back” when you encounter an old friend  Sensation & Perception The flow of information from the outside physical world (Distal stimulus) to the internal mental world (Proximal stimulus) Via the sense receptors - Eyes, ears, skin, tongue, nose Getting information into the system Most people are vision-dominant Humans use vision to navigate, locate objects, recognize objects, and plan actions  Visual Information Processing Visual perception can be divided into - an early phase, in which shapes and objects are extracted from the visual scene, and - a later phase, in which the shapes and objects are recognized Low-Level Vision Decomposition occurs at the lowest level The brain does not receive raw data, but processed information A schematic representation of the eye Light enters through the cornea passes through the aqueous humor, pupil, lens, and vitreous humor then strikes and stimulates the retina Network of Photoreceptors retina contains receptors that react to light energy and change it into Electro-chemical energy  Rods Millions of rods located near the outer edges of the retina Used for detecting dim light Can’t see in colour Connected to the next layer of bipolar cells at the ratio of 20:1 - High sensitivity  Cones Located in the fovea region Needed for colour vision Needed for high detail Connected to next layer of bipolar cells at a ratio of 3:1 Cone system has high acuity cones primarily at fovea where light is focused by muscles controlling lens blind spot is where optic nerve exits eyeball  Different cones are sensitive to different colours cones respond best to certain wavelengths, & less to nearby wavelengths  Massive Parallelism Processing occurs at all stages constantly From retina to ventral & dorsal pathways  Receptive Fields At each step in the Visual Pathway the cells have Receptive fields Receptive field - pattern of light energy to which the cell responds best - Hubel & Wiesel: single-cell recording, 1981 Nobel Prize On-center and Off-center cells On-off and off-on fields of centre- surround cells: ganglion cells and the cells in the lateral geniculate nucleus  Lateral Geniculate Nucleus Receptive Fields in the Primary Visual Cortex (a) and (b): edge detectors respond positively to light on 1 side of a line and negatively to light on the other side (c) and (d): bar detectors respond positively to light in the center and negatively to light at the periphery, or vice versa  Lateral No Lateral End Inhibition Inhibition Stopped What the System “Knows” The arrangement of the eye, the receptors and other visual cells process information without “knowing” what they are processing Location - where on the retina - which eye What the System “Knows” Orientation, movement, and size - Simple + complex cells  What the System Knows Colour - Different cones: Short, Medium, Long wavelengths None of this information requires cognition - although there is top-down processing - even quite early in the visual system (V1) Not just passively processing light What you "see" is interpreted using cognition  Localization and Depth Where are objects in the visual scene? Does the scene involve depth? Types of Depth Perception - Monocular (pictorial) Cues - Binocular Cues  Pictorial Depth Cues Rely on knowledge and tacit assumptions about the world Interposition and Occlusion  Shading shadow at top of circle = a dent shadow at bottom of circle = a bulge Art manipulates pictorial cues street-art chalk drawing on a flat (and entirely undamaged) sidewalk Perceived Distance & Retinal Size Cues combined with knowledge about the size of things in the world Monsters are the same size on 2-dimensional screen Distance creates illusion of "distant" monster being larger Aerial Perspective Linear Perspective Retinal and familiar size give rise to size constancy illusions  Binocular cues Each eye perceives the scene at a slightly different angle Retinal disparity is a powerful indicator of depth https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0020162 #pone.0020162.s012 Daniel Kish (from the video) is blind but relies on echolocation. Check out the “Batman” episode by This American Life, and additional podcast by Invisibilia from NPR