Visual search
Determine when a target appears to pop out of a display, and when it must be searched for item by item.
Method
Procedure
- Each display shows 4, 12 or 24 bars. Look for a red vertical bar; it is present on half of the displays.
- Round 1 (18 displays): the other bars are green, so the target differs from them in colour alone.
- Round 2 (18 displays): the other bars are green and vertical or red and horizontal, so only the combination of colour and orientation identifies the target.
- Each display stays until you answer, or for up to 6 seconds.
Responses
- J
- present: the red vertical bar is there
- F
- absent: it is not
- Touch
- the Present and Absent buttons
Measures
The search time on correct trials at each number of bars, and the slope: how many milliseconds each additional bar adds. A slope near zero means that the number of bars hardly matters and the target pops out; a clearly positive slope suggests that attention moves from item to item.
Practice
Six practice displays of 12 bars, of both kinds, tell you after each one whether the target was there.
The task relies on red and green, so it may not work as intended for people with a colour-vision difference.
Terms
- Feature search: Search for a target that differs from all other items in one simple property, such as colour.
- Conjunction search: Search for a target defined by a combination of properties, each of which is shared with some other items.
- Set size: The number of items in the display.
- Search slope: The extra time taken for each additional item, in milliseconds per item.
- Attention: The selection of some information for further processing at the expense of other information.
- Parietal lobe: The part of the cerebral cortex at the top and back of the head, involved in directing attention.
Experiment
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Results
Interpretation
Compare the two slopes. The usual result, on which feature-integration theory was built (Treisman and Gelade, 1980), is a slope close to zero in round 1 and a clearly positive slope in round 2. Displays with and without the target are combined. Displays without the target often take longer, because more items must be checked before the target can be judged absent.
Limitations
Each slope rests on three set sizes with six displays at each, so it is a rough estimate. The size of the screen changes the spacing of the bars, and the task may not work as intended for people with a colour-vision difference.
The result comes from one person in one session, on a device whose timing and display are not calibrated. It describes this run, not a stable characteristic of the participant, and a second run could differ by chance alone. Research studies test many participants under controlled conditions and report the average with its variability. The experiment is educational; it is not a test of ability or health.
One row per display: round (feature or conjunction), trial, number of bars, whether the target was present, your response, reaction time, whether it was correct and whether it was used in the medians. In the file, 1 means yes and 0 means no. The file is created on this device and can be opened in a spreadsheet.
Background
Original findings
Treisman and Gelade (1980) found that a target that differs from its neighbours in a single feature, such as colour, is found almost as quickly among many items as among a few: it appears to “pop out”. When the target is defined only by a combination of features, search time increases with the number of items, as if attention must move from one item to the next. Their feature-integration theory proposes that attention is needed to combine features such as colour and orientation into a single object.
Neural basis
Attention is directed by networks in the parietal and frontal lobes. One of them, which includes the intraparietal cortex and the superior frontal cortex, guides goal-directed selection such as a deliberate search (Corbetta and Shulman, 2002).
References
- Treisman, A. M., & Gelade, G. (1980). A feature-integration theory of attention. Cognitive Psychology, 12(1), 97–136. https://doi.org/10.1016/0010-0285(80)90005-5
- Corbetta, M., & Shulman, G. L. (2002). Control of goal-directed and stimulus-driven attention in the brain. Nature Reviews Neuroscience, 3(3), 201–215. https://doi.org/10.1038/nrn755
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