Learning to blink at a tone

Introduction: A gentle puff of air to the eye makes people blink automatically. Researchers studied how people come to blink in response to a tone that signals the puff, what happens when the tone stops being followed by the puff, and what happens after a day's rest.

Participants: Forty-eight undergraduate students aged 18 to 24 (27 women and 21 men) at a university in Seoul, South Korea, took part for credit in an introductory psychology course. Students could earn the same credit by writing a short paper instead. People who wore contact lenses or had an eye condition did not take part.

Method: A university ethics committee approved the study, and each participant gave written informed consent and was told they could stop at any time without losing credit. Participants watched a silent film while wearing headphones and a lightweight headset that held a small tube near one eye. The tube could deliver a gentle puff of air, set at a strength each participant had rated as not painful. An infrared sensor recorded every blink.

On day 1, participants were randomly assigned to one of two groups (24 per group). Both groups received 60 tones (each lasting 1 second) and 60 air puffs. In the paired group, every tone was followed by an air puff that arrived just as the tone ended. In the unpaired group, the tones and puffs came at random times, always at least 10 seconds apart. Next, both groups heard 30 tones with no air puff. On day 2, 24 hours later, both groups returned and heard 10 more tones with no air puff.

A conditioned blink was a blink that began after a tone started but before the moment when an air puff would arrive. For each block of trials, the researchers calculated the percentage of tones on which each participant made a conditioned blink. At the end of day 2, participants were told the purpose of the study.

Results and Discussion: The table shows the mean percentage of tones followed by a conditioned blink. At the end of the 60 tone-and-puff trials, the paired group blinked to the tone far more often than the unpaired group, a statistically significant difference. The two groups did not differ significantly in the first 10 trials.