When riding on a bus or the subway these days, I tend to be surrounded by people who seem to exist in a different space. With vacant eyes, they look like they have successfully separated themselves from their perceptual environment. The secret weapon against outside intrusion of their own thoughts seems to be a set of earphones.

As someone who usually tracks people’s eye movements to get a better notion of how we attend to our visual world, it is hard to imagine eyes that don’t move for the purpose of information gathering, but are merely a by-product of attending to inner thoughts.

Schäfer and Fachner recently published a paper in Attention, Perception, & Psychophysics, a journal of the Psychonomic Society, in which they took a closer look at participants’ eye movements while they listened to music. Previous data from subjective reports had shown that “music causes attention to turn away from the environment (exogenous stimuli) and toward inward experiences (endogenous stimuli)”, sometimes even described as “space ceasing to exist”.

Schäfer and Fachner wanted to provide empirical data on how music evokes “physiological changes in the processing of visual information” by investigating the role of attention.

Attention and eye movements are tightly coupled. Schäfer and Fachner therefore measured eye movements as a sort of window to the music-incubated mind. The reasoning behind this is as follows: If music causes attention to turn “inward”, then the external world should become less important. If the external world becomes less important, there is less need to explore it, which again would result in a reduced need to move our eyes (i.e., fewer saccades) or even keep them open (i.e., more blinking).

In addition, Schäfer and Fachner reasoned that someone’s favorite music should be more absorbing than just any kind of music, thus directing attention toward inner thoughts and emotions even further. To test this, they had participants look at a picture or watch a short video clip while either listening to (1) neutral instrumental music (the non-disturbing, lounge kind), (2) their favorite music (which participants were asked to bring along to the study), or (3) no music at all.

The authors’ hypotheses were only party confirmed: When listening to music, “participants exhibited longer fixation durations, fewer saccades, and more blinks than when they viewed the same stimuli in silence.” This was seen as evidence for a shift from external, exogenous to inward, endogenous attention under the influence of music.

So if we attend less to our environment and more to our inner thoughts under the influence of music, does this mean that listening to the radio while driving your car is actually a music-induced hazard? The authors caution to make such a generalization, because the participants in their study did not have a task other than to enjoy the music. If driving your car is your primary task, it may therefore not suffer from musical enjoyment.

The lack of a secondary task, however, also means that an attentional shift per se was not directly tested in this study. Moving the eyes to a lesser degree might not necessarily mean that we are less responsive to our environment. There have been reports that music can actually help prevent inattentional blindness by loosening the attentional focus from a visual task.

Also, against Schäfer and Fachner’s expectations, the effect of music on eye movement activity was not more pronounced when the music was preferred, despite the listeners rating their favorite music as being more absorbing than the neutral music. The lack of any observed differences in eye movements between the two music conditions is difficult to interpret though. The “neutral music” in their study was instrumental, whereas the favorite music that participants brought along was not controlled for its verbal content. It should matter whether the music you are listening to contains lyrics or is purely instrumental. We know, for example, that background speech captures much more attention than background music.

Back to my fellow commuters: The degree to which music allows them to turn away their attention from the outside world towards inner thoughts and emotions is certainly influenced by them listening to music via headphones (as the participants in this study). There is a reason why in some states it is against the law to wear headphones while driving (see AAA’s “Digest of Motor Laws).

Schäfer and Fachner therefore report an interesting result when they show that music seems to turn us into less active visual explorers. While “vision for action” has received a lot of attention over the years, we do spend a good part of our day thinking about bare necessities like what to get for lunch or which of the papers published in one of the Psychonomic Society journals to read next. “Vision for thought” remains an interesting way of looking at cognition.