Drinking More Likely to Leave You with Visual Blind Spots

Drinking too much can result in a form of myopic vision where a person is less likely to see a visual object right in front of his or her eyes, suggests a study appearing in the journal Psychopharmacology.

The clinical term for the narrowed vision is inattentional blindness, or what researchers describe as “the common human failure to perceive a novel but unexpected visual object in plain view when attention is otherwise engaged.”

A new study found that this phenomenon is heightened when a person is intoxicated, according to a team of researchers from University of Portsmouth and University of Winchester in the United Kingdom.

“There is a good deal of evidence supporting alcohol myopia theory, the idea that alcohol consumption depletes attentional resources inducing a form of ‘short-sightedness’ through which only the most central or important environmental cues are processed,” write the researchers in Psychopharmacology.

Perhaps the most famous study to assess inattentional blindness involved having participants watch groups of basketball players pass a ball back and forth. In that study, the researchers instructed the participants to count the number of passes made by a single team of players. But there was a hitch. “A few seconds into the game, an unexpected female in a gorilla suit casually strolls among the players and across the court,” recount the researchers.

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Fewer than half of the study participants – or 44 percent – noticed the woman in the gorilla suit. Among intoxicated study participants, the numbers were even worse. Less than one in five, or 18 percent, of drunken viewers took note of the encroaching gorilla.

For the new study, the researchers upped the ante. They wanted to increase the mental task to find out if there was a threshold of sorts after which alcohol failed to impact a person’s attentional capacity. The researchers stuck to the basketball theme and divided their study participants into an easy and hard group.

“Prior to viewing the clip, each participant was instructed to count, as accurately as possible, either the total number of passes (easy task) or the number of aerial and bounce passes (hard task) made by the white-shirt team, depending on which version of the task they had been assigned,” describe the researchers.

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In the easy version, intoxicated participants fared worse than their sober counterparts. “Results are consistent with alcohol myopia theory. Alcohol intoxication depletes attentional resources, thus reducing the drinker’s awareness of salient stimuli that are irrelevant to some ongoing primary task,” report the researchers.

However, the same effect wasn’t found among the hard task, leaving researchers to theorize that when mental capacity is stretched thin, alcohol intake – or no intake – doesn’t dampen attentional functioning. They think that’s because there’s no further attentional capacity to affect.

“Should this be so burdensome as to consume all of the viewer’s mental resources — such as driving on ice perhaps, or convincing an armed assailant not to shoot — then we expect any additional attentional narrowing effects of intoxication to be negligible, as alcohol cannot drain resources from an empty cognitive reserve,” they write.