Can a demanding visual task make us deaf to sounds?
When people did a hard visual search, they became genuinely worse at hearing a brief tone they were expecting, showing that vision and hearing draw on a shared attentional capacity.
Source
Load-induced inattentional deafness
Study at a glance
- Design
- Human experiment — Four lab experiments manipulating visual perceptual load (letter search with dissimilar vs similar non-targets) while participants detected a brief tone, analysed with signal detection theory; load was varied between participants.
- N
- N=70 · 70 adults across four experiments: 18 in Experiment 1, 18 in Experiment 2, 14 in Experiment 3 and 20 in Experiment 4, each split between low- and high-load groups.
- Population
- Adult volunteers from a UCL participant pool with normal vision and hearing
- Outcome
- Auditory detection sensitivity (d'), hit rates and response criterion (beta), plus visual search reaction time and errors
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What they did
Across four experiments with 70 adults, participants searched a ring of six letters for an X or N. In the low-load version the other letters were small Os; in the high-load version they were similar-looking letters, making search harder. On some trials a brief tone was played and participants had to report whether they heard it. Later experiments had people respond to the tone first, made the tone appear on half of trials with a present/absent answer required every time, or removed background white noise, to rule out alternative explanations.
What they found
In all four experiments, high visual load lowered auditory detection sensitivity (d') compared with low load, not just the response criterion. When incorrect search trials were included in Experiment 1, correct detection fell from about 81% under low load to 44% under high load. The effect held when the tone response came first, when the tone was expected on half of trials, and when there was no background noise, although it looked smaller without noise. Participants who were more efficient at the visual search also detected tones better, and prior lab experience did not change the effect.
The limits
What it doesn't show
Load was manipulated between participants with small groups (only about seven to ten people per load condition), so individual differences could contribute and the effect sizes are imprecise. The tasks were simple lab stimuli (letters and a pure tone over headphones), so the applied examples such as pedestrians missing an approaching car are extrapolations rather than tested outcomes. The study only tested visual load affecting hearing, not the reverse, and the authors note that auditory load does not always affect vision. The individual-differences analysis used a median split, which is a coarse, correlational test of the shared-capacity idea.
Key terms
- Perceptual load theory
- Lavie's theory that perception has limited capacity: when a task uses up most of it (high load), little is left over to process other stimuli.
- Inattentional deafness
- Failing to hear a clearly audible sound because attention is taken up by another task, the auditory counterpart of inattentional blindness.
- d' (d-prime)
- A signal detection measure of how well someone can tell a signal from its absence, independent of how willing they are to say 'yes'.
- Response criterion (beta)
- A signal detection measure of bias: how much evidence a person needs before reporting that a signal was present.
- Goal neglect
- Forgetting or failing to act on one of the task goals, such as simply not bothering to respond to the tone when the main task is hard.
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Quiz yourself
What made the high-load visual search harder than the low-load search?
Common questions
Why does it matter that they measured d' rather than just asking whether people noticed the sound?
Earlier studies used a single surprise question, so people might have heard the sound but forgotten it or been cautious about saying yes. Measuring d' across many trials separates true sensitivity from bias, showing that high load actually reduced how well the tone was perceived.
How did they rule out memory as an explanation?
In Experiment 2 participants responded to the tone immediately, before making the visual search response, so there was no delay in which the tone could be forgotten. The load effect on detection was just as strong.
Does this mean hearing and vision use exactly the same resource?
The results suggest they share some attentional capacity, because visual load reduced auditory sensitivity by a similar amount to its effect on visual detection in earlier work. But the authors note that auditory load does not always harm visual perception, so the sharing may depend on the situation.
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