Macdonald, J. S., & Lavie, N. (2011). Visual perceptual load induces inattentional deafness. Attention, Perception, & Psychophysics, 73(6), 1780-1789.
This seems to me to be the first paper on the subject, dating from 2011. The idea was to verify whether perceptual capacity is modality specific or not. The method was rather simple and low-tech, which is different from what I have been reading. And refreshing for that matter! Once again, the authors – who first brought attention to the inattentional deafness concept – modified an inattentional blindness paradigm to assess inattentional deafness.
The authors say that focused attention on a task results in reduced perception of irrelevant information. This reduction depends on the level of the perceptual load in the task. Perceptual load corresponds to the amount of information involved in the perceptual processing of the task stimuli. Tasks involving higher perceptual load consume all or most of attentional capacity, leaving little or none remaining for processing any task irrelevant information. In this scenario, the authors ask, would a car horn be noticed when you were attending to a visually loaded billboard?
They wanted to see whether perceptual load in a visual attention task would modulate conscious awareness of task unrellated auditory tones.
For that, a set of three experiments were made, all with a very similar set-up and procedure.
In the low load task, the participant had to signal which arm of the cross was blue.
In the high load task, the participant had to signal which arm was longer. By the end of the eighth trial, a critical audio sign (CS) was played, and by the end of the task the participant was asked if s/he noticed anything different from previous trials.
For experiment 1, white noise was played continuously for 19s during each trial. In the critical and control trials, a 180 Hz pure tone at 28 dB of either 100 or 150ms was presented at the onset of the cross.
The participants were later asked to describe the experiment, even when they have not noticed anything different.
The results demonstrated that error rates were significantly higher in the high load condition than in the low load condition. 7 out of 28 participants reported awareness in the high load condition, whereas 21 out of 28 noticed something different in the low load condition. These results show that, in fact, the tasks differed as for mental load, and what’s more, that the effect of inattentional deafness was indeed verified.
Experiment 2 wanted to assess to what extent could the phenomenon be verifies, so the authors removed the white noise, leaving the critical audio sign unmasked.
Again, both high and low load conditions differed significantly in error rates. In the high load 5 out of 24 noticed the sign, and in the low load, 21 out of 24 noticed it.
This means that high perceptual load in a visual attentional task reduces auditory awareness, thereby producing inattentional deafness, even with an unmasked tone and when people are not actively ignoring sound.
Experiment 3 randomly intermixed the high and low task within a longer block of 143 trials. Also, the low load task was changed to a line length discrimination task with a far greater line length difference than in the high load condition. Like in experiment 2, no white noise was played.
In this experiment, the reaction times were significantly longer in the high load condition, and error rates were also higher in the high load condition. 18 out of 32 reported awareness in the high load condition, and 28 out of 32 reported it in the low load condition. These surprising results got the authors to the conclusion that inattentional deafness was influenced by the level of visual perceptual load in the task rather than by any differences in motivation, vigilance, task engagement, or strategy.
All in all, results suggested that the elementary process of noticing the mere presence of a sound depends on an attentional capacity resource that is shared between the modalities of vision and hearing.
The authors claim that it is possible that some processing capacities are modality specific, while others draw on a shared cross-modal resource. For example, previous findings that perception of visual motion is reduced by attention to a high load visual stimulus stream, but not to an auditory word stream, may indicate that the perception of visual motion suffers from visual capacity limits.