Thursday, December 10, 2015

Visual effort and inattentional deafness

Visual Effort and Inattentional Deafness

Earlier this week I was asked for my thoughts on a new Journal of Neuroscience paper: 
Molly, K., Griffiths, T. D., Chait, M., & Lavie, N. (2015). Inattentional deafness: Visual load leads to time-specific suppression of auditory evoked responses. Journal of Neuroscience, 35, 16046-16054.doi: 10.1523/JNEUROSCI.2931-15.2015
In part due to a widely circulated press release, the paper has garnered a ton of media coverage, with headlines like:
Focusing On A Task May Leave You Temporarily Deaf: Study

Did You Know Watching Something Makes You Temporarily Deaf?

Study Explains How Screen Time Causes 'Inattentional Deafness'

The main contribution of the paper was a link between activation in auditory cortex and the behavioral finding of reduced detection of a sound (a brief tone) when performing a more difficult visual task. 

This brain-behavior link, not the behavioral result, is the new contribution from this paper. Yet, almost all of the media coverage has focused on the behavioral result which isn't particularly novel. That's unsurprising given that most of the stories just followed the lede of the press release, which was titled:
"Why focusing on a visual task will make us deaf to our surroundings: Concentrating attention on a visual task can render you momentarily 'deaf' to sounds at normal levels, reports a new UCL study funded by the Wellcome Trust"

Here are a few points about this paper that have largely been lost or ignored in the media frenzy (and the press release):

1. The study did not show that people were "deaf to their surroundings." In the study (Experiment 2), people performed an easy or hard visual task while also trying to detect a tone that occurred on half of the trials. When performing the easy visual task, they reported the tone accurately on 92% of the trials. When performing the harder visual task, they reported it accurately on 88% of trials. The key behavioral effect was a 4% reduction in accuracy on the secondary, auditory task when the primary visual task was harder.  In other words, people correctly reported the tone on the vast majority of trials even with the hard visual task. That's not deafness. It's excellent performance of a secondary task with just a slight reduction when the primary task is harder. 

Aside: much of that small effect on accuracy could be due to a difference in response bias between the conditions (Beta of 3.2 compared to 1.3, a difference reported as p = 0.07 with an underpowered study of only 11 subjects).

2. The behavioral effect of visual load on auditory performance is not original to this paper. In fact, it has been reported by the same lab.

3. A number of other studies have demonstrated costs to detection in one sensory modality when focusing attention on another modality. This paper is not the first to show such a cross-modal effect. See, for example, hereherehereherehere (none of which were cited in the paper). Many other studies have shown that increasing primary task difficulty decreases secondary task performance. Again, the behavioral result touted in the media is not new, something the press release acknowledges in passing.

4. The study doesn't actually involve inattentional deafness; the term is misused. Inattentional deafness or blindness refers to a failure to notice an otherwise obvious but unexpected stimulus when focusing attention on something else. The "unexpected" part is key to ensuring that the critical stimulus actually is unattended (the justification for claiming the failure is due to inattention); people can't allocate attention to something that they don't know will be there. 

In this study, tone detection was a secondary task. People were asked to focus mostly on the visual task, but they also were asked to report whether or not a tone occurred. In other words, people were actively trying to detect the tone and they knew it would occur. That's not inattentional deafness. It's just a reduction in detection for an attended stimulus when a primary task is more demanding. And, as I noted above, it's not really a demonstration of deafness either given participants were really good at detecting the tone in both conditions (they were just slightly worse when performing a harder visual task). 

Note that the same lab previously published an paper that actually did show an effect of visual load on inattentional deafness.

ConclusionThere's nothing fundamentally wrong with this paper, at least that I can see (I'm not an expert on neuroimaging, though). The link between the behavioral results and brain imaging results is potentially interesting. I would have preferred a larger sample size and ideally measuring the link between brain and behavior in the same participants performing tasks with the same demands, but those issues aren't show stoppers. I can see why it is of interest to specialists (like me). That said, I'm not sure that it makes a contribution of broad interest to the public, and the novelty and importance of the behavioral result has been overplayed.


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  21. I remember a study about auditory phenomenon by tackle of the same process.