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PSYC2030 - Sensation and Perception Chapter 8

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York University
PSYC 2220
Jennifer Steeves

Lecture 8 Attention and Scene Perception Attention • Selective attention: The form of attention involved when processing is restricted to a subset of the possible stimuli Selection in Space • Curing as a tool for examining attention o Posner cueing paradigm o Simple probe detection experiment o Cues are valid or invalid  RTs are shorter on valid cue trials  RTs are longer on invalid cue trials Disorders of Visual Attention • Visual field defect: A portion of the visual field with no vision or with abnormal vision, typically resulting form damage to the visual nervous system • Parietal lobe: In each cerebral hemisphere, a lobe that lies toward the top of the brain between the frontal and occipital loves o Damage to the parietal lobe can cause a visual field defect such that one side of the world is not attended to o Also affects visual imagery • Neglect o Uses top-down knowledge to help deal with their visual deficiency o The inability to attend to or respond to stimuli in the contralesional visual field  Typically, neglect of the left visual field after damage to the right parietal love  Contralesional field: The visual field on the side opposite a brain lesion • For example, points to the left of fixation are contralesional to damage to the right hemisphere of the brain  Ipsilesional field: The visual field on the same side as a brain lesion o There is no such thing as right-neglect, only left o The right hemisphere of the brain has more spatial representation (causes left-neglect) Spotlight Theory • Egly, Rafal & Driver (1994) • Spotlight prediction: o Fastest RTs for 1 o RT for locations 2 = 3 Theories of Attention • “Spotlight” model: Attention is restricted in space and moves from one point to the next. Areas within the spotlight receive extra processing • “Zoom lens” model: The attended region can grow or shrink depending on the size of the area to be processed Selection of Objects • Attentional benefit observed at a novel location on a cued object • Attentional benefit observed for a cued object that has moved to a new location • Superimposition – selection of one of two objects that occupy the same spatial location Disorders of Visual Attention • Attention can be object-based o Evidence from neglect patients indicates that they sometime neglect one side of an object rather than one side of the visual field Visual Search • Visual search Task: Report the presence/absence of a target in a display containing distracting elements o Target: The goal of a visual search o Distractor: In visual search, any stimulus other than the target o Set size: the number of items in a visual search display • The efficiency of visual search is quantified as average RT as a function of set size o Measured in terms of search slope, or ms/item o The larger the search slope (more ms/item), the less efficient the search o Some searches are efficient and have small slopes o Some searches are inefficient and have large slopes • Guided Search A search in which attention can be restricted to a subset of possible items on the basis of information about the target item’s basic features (e.g., its colour) • The blinding problem: The challenge of typing different attributes of visual stimuli, which are handled by different brain circuits, to the appropriate object so we perceive a unified object o Example: A vertical red bar moving to the right • Colour, motion, and orientation are represented by separate neurons • How do we combine these features when perceiving the bar? • Feature integration theory: o Limited set of basic features can be processed in parallel preattentively o But other properties, including the correct binding of features to objects, require attention o Preattentive stage: The processing of a stimulus that occurs before selective attention is deploy
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