PSYC10003 · Mind, Brain and Behaviour 1
Visual Attention and Object & Scene Perception
Week 9 opens the Sensation & Perception strand: how selective visual attention gates awareness, and how the visual system builds objects and scenes from features. It centres the required reading (Rensink, O'Regan & Clark, 1997) and the change-blindness phenomenon, and covers Feature Integration Theory, feature-versus-conjunction search, and Gestalt grouping. The examinable skill, within the 25% Sensation & Perception block, is explaining top-down versus bottom-up processing and why change blindness reveals the limits of visual awareness.
What this chapter covers
- 01Attention as preferential processing under limited capacity; overt vs covert attention
- 02What directs attention: bottom-up capture by salience (contrast) vs top-down goals and expectations
- 03The binding problem and Feature Integration Theory (attend to one location to bind features)
- 04Feature search (pop-out, set-size independent) vs conjunction search (serial, set-size dependent)
- 05Illusory conjunctions when attention is inhibited; Balint's syndrome
- 06Change blindness: failure to notice an unattended change that seems obvious in hindsight
- 07The flicker paradigm (Rensink et al. 1997): a blank field masks motion transients → change blindness
- 08Gestalt grouping principles; figure-ground segregation; gist perception
Predicting search performance and explaining change blindness
- +1(a) Display A is a feature search: the target differs by a single feature (colour), so it pops out — search is fast and roughly independent of the number of distractors (no binding needed).
- +1Display B is a conjunction search: the target shares features with the distractors and is defined only by the particular combination (red AND vertical), so attention must be applied item by item — search is slow and reaction time rises with set size.
- +1Name the theory. Feature Integration Theory explains this: single features are registered in parallel across the field, but binding features into objects requires focal attention to one location at a time, which makes conjunction search serial.
- +1(b) Explain change blindness. Normally a change creates a local motion transient (flicker) that automatically draws attention to its location. The blank field inserted between images creates transients everywhere at once, so transients no longer single out the change; unless the changing region happens to be attended, the change is missed.
Key terms
- Selective attention
- The preferential processing of some parts of a scene at the expense of others, needed because the perceptual system has limited capacity and cannot process everything at once.
- Bottom-up vs top-down
- Bottom-up (stimulus-driven) attention is captured by salient features such as contrast; top-down (goal-driven) attention is directed by the observer's goals and expectations. Both shape where we look.
- Feature Integration Theory
- Treisman's account in which individual features are detected in parallel but must be bound into objects by focal attention to one location — explaining why conjunction search is serial and illusory conjunctions occur when attention is diverted.
- Feature vs conjunction search
- Feature search (target differs by a single feature) produces fast, set-size-independent pop-out; conjunction search (target defined by a combination of features) requires serial, attention-demanding search whose time grows with set size.
- Change blindness
- The failure to notice a change to a scene that seems obvious in retrospect, occurring when the change falls outside attention or when motion transients that would flag it are masked.
- Gestalt grouping
- Principles by which the visual system organises elements into wholes — good continuation, similarity, proximity, common fate, common region — the more that apply, the stronger the grouping.
Visual Attention and Object & Scene Perception FAQ
What is the difference between bottom-up and top-down attention?
Bottom-up attention is captured involuntarily by salient stimulus properties — high colour, luminance, size or motion contrast. Top-down attention is directed voluntarily by your goals and expectations, so what you look at depends on the task. Early fixations tend to be bottom-up; later ones are increasingly top-down.
Why does change blindness happen?
Because you can only hold a few parts of a scene in attention at once. Normally a change produces a local motion transient that draws attention to it; if that transient is masked (for example by a blank field in the flicker paradigm, or a cut in a film) or the change is in an unattended region, you fail to notice it. It shows attention is necessary to perceive change.
How does Feature Integration Theory explain visual search?
Simple features (like colour) are registered in parallel across the whole display, so a target defined by one feature pops out regardless of how many distractors there are. Binding several features into an object requires focal attention to one location at a time, so a conjunction target must be searched serially and reaction time grows with set size. Diverting attention produces illusory conjunctions.
What is the required reading for this section?
Rensink, O'Regan and Clark (1997), a change-blindness study using the flicker paradigm, is the required reading, and the Week 11 practical is based on it. Revise it as a demonstration that attention is needed to detect change, not as a set of dates.
How is Sensation & Perception examined?
Almost entirely as findings-style multiple-choice questions — a study is described and you identify what it showed, or a phenomenon is described and you name the mechanism. There are no calculations in this strand; the marks go to clean conceptual distinctions like feature vs conjunction search or bottom-up vs top-down.
Exam move
Anchor the strand on two distinctions: bottom-up vs top-down attention, and feature vs conjunction search (pop-out vs serial). Be able to predict a search slope from the display and to explain change blindness through masked motion transients rather than vague 'not paying attention'. Learn the Gestalt grouping principles as a checklist you can apply to an example, and revise the Rensink flicker reading as a mechanism. Because this block is entirely conceptual MCQs, practise turning described studies into 'what it shows' one-liners. Confirm exam details on Canvas.
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