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Lecture 6

PSY270H1F Lecture 6

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University of Toronto St. George
Kristie Dukewich

PSY270H1F L6; Oct 24, 2012  Have “top-down” knowledge after knowing it’s of C3P0 & Princess Leia Object Recognition Feature Detectors  Hubel & Wiesel: feature detectors  Neurons in visual cortex that respond to features that make up objects  Dif neurons respond to dif features o Lines, edges, basic shapes, angle/orientation, Announcements movement (major factor)  Essay & Turnitin info online o  comes to represent object in brain you’re looking o Your original writing should not have much highlighting at in it  Background prob from textbook – cite it! o Use to define o Define everything in your paper! o Only need to use paper & textbook as sources  Holistic marking scheme – qualitative  Cannot get perfect if you use ANY quotes  Read the assignment at least 3-4 times, before, during, & after your essay to make sure you’re answering the question o Listened into dif nerve cells of anesthetized cat Expt  Visual avging of #s, shown for 100ms o Tried to make cells fire (single-cell recordings) o Shined small spots (white or black) onto screen  black dot moved across screen moved thin line of edge of slide Ch. 3: Perception  Top-down vs bottom-up processing across retina – cells fired, responded to the thin line o Object recognition  Accidental discovery o Gestalt Psychology Recognition by Components o Regularities  Interactions btwn perceiving & taking action  Irving Biederman: recognition of objects = based on 3D o What/ where pathways features  Similar to Hubel & Wiesel’s feature detectors but now at Iclicker bhvr’al level  Iconic memory & elaborative rehearsal are 2 of the concepts  Geons – basic feature units, perceptual building blocks o Described 36 that comprise all the objects we interact w we learned about while covering memory.. Are they related to “bottom-up” or “top-down” processing? o Compared w representations in memory  object  Iconic: “Bottom-up” recognition  Elaborative rehearsal: “Top-down” Bottom-up vs Top-down  Top-down: processing that starts w knowledge, experience, expectations o Help us make sense of things we’re looking at  Bottom-up: processing that starts w incoming sensory info  Prediction: If objects are parsed in geons, then object recognition should be a fn of the # of geons available  Varied total # of geons a person could see & still recognize the object  Airplane = 9 constituent geons o 3 available: recognition = 78% o 6 available: recognition = 96%  Had no “top-down” knowledge before seeing this pic, so use “bottom-dow”  1 to emphasize top-down processing  If prevent pp from recognizing geons, can prevent ppl from  Laws of perceptual organization recognizing full object o Proposed rules to explain how small elements of a scene are grouped to form larger units o Law of Good Continuation: we tend to grp together elements that form smooth & continuous lines  Generally not interpreted as 4 lines or 2 wings, instead see 2 continuous smooth lines crossing each other Gestalt law of... (similarity, familiarity, proximity, closure, common fate, simplicity)  Laws generally found everywhere Simplicity – assume the simplest structure (vs 9 weird shapes grped together) Good Continuation Proximity – grp objects near one another o Top: Need corner-type info to tell what geon it is o Same flashlight image amt available in each figure Closure – o So harder to recognize top figure compared to bottom figure 1: things that form closed shapes are grped together; 2: even when there’s an incomplete figure, Top-down Influences we tend to close it (ex. It cut out a little piece)  Geons are bottom-up, but top-down processing always influences object recognition (because geons are familiar Similarity – grp alike things objects) Common fate – things moving in same direction are grped together (dots moving towards each other) Familiarity – things that are familiar or o The blobs are actually from dif pics – not a person meangful to us are likely grped together standing, not a car driving o What it is, is d
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