MCAT content library / Psychology & sociology / Attention under competing task demands
A second task can change accuracy, response time, or both. Use the task demands and the comparison to explain the cost.
About 17 minutes, including the worked examples and checks.
On this page
- Define the competing demands before judging attention
- A distractor’s presence is different from its processing demand
- Worked experiment: keep the sounds, change the job
- Read speed together with accuracy
- Distinguish resource allocation from a global change
- Build the explanation from the comparison
- Check your reasoning
- Continue learning
- Sources
Define the competing demands before judging attention
“Performance fell while multitasking” leaves several questions unanswered. Which task fell? Did responses become slower, less accurate, or both? Did the second task compete for sensory input, a decision, a remembered rule or a response? AAMC places selective attention, divided attention and information-processing models together because the task structure helps explain the observed cost.1
Selective attention prioritizes relevant information while competing information is present. Divided attention involves meeting more than one task demand. These are descriptions of what the participant must do, not two scores that can be read directly from a single button press.2 A person ignoring tones while sorting shapes faces a different instruction from a person required to classify both tones and shapes.
A distractor’s presence is different from its processing demand
In the classic color-word task, a person may need to name ink color while a printed color word supplies a conflicting response. Stroop’s original experiments compared the interference associated with the different task dimensions.3 The relevance of the word depends on the instruction: it is central when reading and a distractor when naming ink color.
This distinction prevents an easy error. If two conditions contain the same physical sounds, the sensory stimulation is matched, but the required processing may not be. One condition may instruct the participant to ignore the sounds; another may require a decision about each sound. Conversely, comparing a quiet task with a dual task changes both the acoustic environment and the task requirement.
An information-processing account separates useful stages such as encoding a stimulus, identifying its category, selecting a response and executing that response. These are model components, not a claim that all cognition follows one rigid serial chain. Different tasks may interfere at different stages. Research on dual-task performance distinguishes response-selection limits from effects of preparation, perception and timing.5
Worked experiment: keep the sounds, change the job
The tasks and data in this lesson are original teaching examples. Participants classify a central visual symbol with one hand. In three conditions, the same audible tone sequence accompanies the visual symbols. The tones are well above each participant’s measured detection threshold. Block order is counterbalanced, and the visual display, response mapping and number of trials are held constant.
When tones must be classified, participants use the other hand. The easier auditory task classifies the current tone as high or low. The harder task reports whether the current tone is higher or lower than the preceding one. Its first tone establishes a reference rather than requiring a comparison response.
| Condition | Visual accuracy | Visual response time, correct trials | Auditory accuracy |
|---|---|---|---|
| Visual task alone | 96% | 500 ms | Not required |
| Same tones; ignore them | 96% | 515 ms | Not required |
| Classify current tone | 94% | 590 ms | 95% |
| Compare with preceding tone | 91% | 690 ms | 86% |
The comparison between ignoring and classifying the same tones holds their physical presence constant. Classifying the current tone is associated with a 590 − 515 = 75 ms visual slowing and a 2 percentage-point visual accuracy decrease. Comparing successive tones is associated with a 175 ms slowing and a 5 percentage-point decrease relative to ignoring them.
The harder auditory task also has lower auditory accuracy. It is therefore not sensible to report only that “the visual task got worse”: both outcomes help characterize the competing demands. The table is descriptive; without participant-level variation and an uncertainty analysis, these differences do not establish statistical significance.
The matched-sound comparison rules out an explanation based solely on tones being physically present. It does not isolate one cognitive mechanism, because requiring an auditory judgment also adds a decision and a motor response. A follow-up could preserve the auditory response while simplifying the decision, or change response modality while keeping the categorization rule fixed. The relevant control depends on the particular alternative being tested.
Read speed together with accuracy
Consider another block in which an instruction emphasizes speed. Visual responses shorten from 690 to 550 ms, but accuracy falls from 91% to 82%. The participant is faster, yet the observation does not show an unqualified improvement. It is compatible with accepting more errors to respond sooner.
A reaction-time average also needs its sampling rule. The worked table reports correct trials only. If a condition produces many more errors, the remaining correct trials may not represent the same difficulty mix as before. Report the accuracy alongside the time measure, and retain the same response deadline and rules for exclusions when comparing conditions.
A combined score can be useful if a task specifies how speed and errors are valued. It cannot supply those values by itself. Dividing percent correct by milliseconds, for example, creates a new index whose interpretation must be justified; it does not automatically measure a single attention capacity.
Distinguish resource allocation from a global change
Suppose the displays and tasks remain identical but participants are told to prioritize vision. Visual accuracy might increase while auditory accuracy decreases. That pattern is consistent with a change in how task priorities are implemented. It does not show that the person has acquired a larger capacity for both tasks.
A bottleneck account makes a more specific claim than “the tasks compete”: under its stated conditions, some operations cannot proceed together, so one must wait. Pashler tested timing predictions that differed from a graded resource-sharing account in a particular two-task paradigm.4 The lesson is to use discriminating predictions. The mere presence of a dual-task cost cannot prove that the bottleneck is at response selection rather than another stage.
Similarly, a person who performs well on one practiced task pair has not demonstrated cost-free performance on every possible pair. The tested stimuli, response rules, practice history and priorities define the evidence. “Attention” becomes more informative when attached to those conditions.
Build the explanation from the comparison
First name the target and the competing demand. Next compare performance with the relevant single-task or matched-input condition. Keep each task’s accuracy and response time separate. Finally ask which manipulation would distinguish sensory distraction, decision interference, motor competition or a priority shift. This sequence turns a general statement about concentration into an explanation that another experiment can challenge.
ACTIVE PRACTICE · DIVIDED ATTENTION
Keep the Tones, Change the Job
The lesson’s controlled tone experiment measures visual accuracy and response time on correct trials. The same audible tone sequence is used whether it must be ignored, classified, or compared with the preceding tone. A separate speed-emphasis block changes the task instruction.
| Visual accuracy | Correct-trial visual RT | Auditory accuracy |
|---|---|---|
| 96% | 500 ms | Not required |
Reference condition; no competing tone judgment.
Original results are descriptive condition means; no variance or inferential significance is supplied. The speed-emphasis row is a separate changed block.
Check your reasoning
Choose an answer before opening its feedback. Each option explains the reasoning behind that choice.
Check 1
The same participants perform the same symbol task under two randomly ordered instructions. Under “be careful,” mean response time is 720 ms with 92% accuracy. Under “be fast,” it is 560 ms with 84% accuracy. Which conclusion best fits these results?
A. The faster instruction demonstrates greater task accuracy because more responses can fit into a minute.
Review this choice. Accuracy is the proportion of responses that are correct, and it fell from 92% to 84%. Possible throughput does not change that measured proportion.
B. The faster instruction eliminates the need to consider errors when comparing performance.
Review this choice. Errors increased. Ignoring them would turn a two-outcome comparison into an unsupported claim of overall improvement.
C. The instruction changes speed and accuracy in opposite directions, so overall improvement needs a stated performance criterion.
Correct. Responses are 160 ms faster but accuracy is 8 percentage points lower. Deciding whether that tradeoff is preferable requires a specified value for time and errors.
D. The slower condition establishes that the participants failed to perceive the symbols in the faster condition.
Review this choice. The data do not locate the source of errors. Perception, decision policy and response execution remain possible contributors.
The principle to carry forward
Keep the direction and units of both outcomes before calling a condition better.
Check 2
A visual task slows when participants must also categorize tones. A proposed explanation is that the tones’ acoustic presence alone causes all of the slowing. Which additional condition most directly tests that explanation?
A. The identical tone sequence is presented while participants perform only the visual task and ignore the tones.
Correct. This holds the acoustic input constant while removing the categorization requirement. A remaining difference would be inconsistent with acoustic presence alone explaining the full cost.
B. The visual display is made brighter while participants continue to categorize the original tones.
Review this choice. This changes visual input but does not isolate the effect of merely hearing the tones from the added auditory task.
C. The tones are removed while participants perform a different, more difficult visual task.
Review this choice. Both sensory input and visual difficulty change. The comparison cannot isolate the proposed acoustic explanation.
D. The tones are made louder while participants continue to categorize them with the same response keys.
Review this choice. This tests a change in sound level during the auditory task, not whether the mere presence of sound accounts for the original dual-task difference.
The principle to carry forward
A matched-input control addresses physical stimulation; further controls may still be needed to separate decision and motor demands.
Check 3
With identical displays and response rules, participants first give equal priority to two tasks and then receive a vision-priority instruction. Visual accuracy rises from 90% to 96%, while auditory accuracy falls from 92% to 80%. Which interpretation is most warranted?
A. A larger general processing capacity has been demonstrated because one task improved.
Review this choice. The other task worsened. One improved outcome is insufficient evidence of a general increase benefiting both tasks.
B. A change in task priority is consistent with better visual performance at an auditory performance cost.
Correct. The instruction and the opposing outcome changes support a priority-dependent tradeoff under these conditions.
C. An auditory sensory loss is established because the tone-classification score decreased.
Review this choice. The same tones and response rules are used, and priorities change. A score decrease does not identify loss of sensory function.
D. An unchanged task balance is established because the stimuli remained physically identical.
Review this choice. Physical matching does not preserve the way participants allocate effort or implement priorities. The instructions and outcomes changed.
The principle to carry forward
A better result on the prioritized task can coexist with a cost elsewhere; retain both outcomes.
Continue learning
Related lessons
- Psychological Measurement: What Does the Score Mean?
- Perceptual organization: features, context, and constancy
- Experimental Controls: What a Comparison Can Show
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Sources
1. AAMC: Content Category 6B — Making sense of the environment
2. Frances Friedrich: Attention — Noba
3. Stroop (1935): Studies of interference in serial verbal reactions
4. Pashler (1994): Graded capacity-sharing in dual-task interference?
5. Pashler (1994): Dual-task interference in simple tasks: data and theory