When you’re talking to someone, you might ask them to try and remember what they had for breakfast two days ago. As they think back, their eye movements will increase.
The movements are non-visual, they don’t actually provide any information about what we can see around us and can occur in the dark or when our eyes are closed. Instead, they appear to be linked to certain aspects our thought processes, such as trying to remember information while we’re talking to someone.
The reason behind these movements is a mystery, as they don’t actually assist us in recalling information. Professor Howard Ehrlichman from The City University of New York has speculated that they may tell us something about how our higher mental functions, such as the ability to search through our memories for information, may have evolved.
Animals that rely primarily on vision such as primates need brain systems that support the search for information in the visual world. “Perhaps these very same systems were adapted through evolution to also permit humans to search through information not just in the external world, but also in the internal world (our memories).”
However, our eye movements continue to be triggered by these internal search systems, such as trying to recall information during a conversation, even though they don’t play any role in the search for or maintenance of information.
During a study into eye movements, Ehrlichman found that when the participants were asked to stare straight ahead and suppress their eye movements, their ability to perform memory search tasks was unaffected. But when they were asked to search through their long-term memories and recall words from a list they had just studied or explain the meaning of a word, their eye movements naturally increased.
This increase could possibly explain why talking on your mobile while driving is a problem. If people make eye movements when they are thinking or conversing, then the movements may interfere with keeping the eyes focused on the road.
The rate of eye movement increase will vary among individuals, as some people will normally make one movement every five seconds and others make as many as three per second. “But regardless of whether a person has a generally low or high eye movement rate, they will still make more eye movements when searching for information in long term memory than when they do not need to search for such information,” Ehrlichman says.
Our brain systems have also evolved to stop our eye movements when something of interest has been located in the visual world. When the study participants were asked to memorise words or mentally go through the alphabet and calculating how many letters have an ‘E’ sound, their eye movements decreased instead.
This was because they weren’t being asked to search through their memories, but were instead focusing on the information that was in their conscious minds or coming in from an external source.
This could tell us whether someone is thinking on their feet and searching for information from their long-term memory to tell them what to say, or simply reciting something they have memorised or repeated many times. Ehrlichman believes that this is still speculation and needs to be tested.