By Emma Young

It’s well-known that we can easily miss objects in our environment that are outside the focus of our conscious attention. “Inattentional blindness” is demonstrated by the famous “invisible gorilla” studies, for example. But there’s a darker side to this phenomenon: if it happens while you’re driving – or if you’re a baggage checker at airport security – the consequences could be fatal.

Now a new paper, by Joshua Eayrs and Nilli Lavie at University College London, published in the Journal of Experimental Psychology, shows that some people can handle more visual information than others before developing this and related kinds of attentional blindness, and this is because they have a greater visual perceptual capacity. “We identified a novel trait that is different from working memory, general intelligence or motivational factors,” Lavie said in a press release.

In initial studies conducted on 279 visitors to the Science Museum in London, Eayrs and Lavie first assessed participants’ perceptual capacity by asking them to rapidly identify the total number of objects in a scene – a so-called “subitizing” task that measures “the simultaneous, parallel processing capacity for detection and individuation of items”. A series of 162 images of between one and nine randomly sized and positioned black squares were presented for 100 milliseconds each. Previous work has found that, on average, people can reliably enumerate about three to four items and a mean of 3.62 was found for this group.

The researchers then found that people who were better at subitizing – suggesting that they have higher perceptual capacity – were also better at identifying whether two photographs, presented briefly in rapid succession, were identical or very nearly identical (that is, they were less susceptible to a form of inattention known as “change blindness”).

In a second study, on 122 more visitors to the Science Museum, the researchers linked a greater subitizing capacity to being less susceptible to “load blindness” as revealed by their superior performance on a task that progressively increased the perceptual load (participants had to try to judge the lengths of lines of an X while also monitoring other changeable elements in the periphery of the scene).

In a third study, the researchers explored whether the superior performance of participants with higher perceptual capacity was simply because they have greater working memory capacity. Working memory describes how much information we can hold and manipulate in mind at any time and it’s a key aspect of cognitive functioning that is known to underlie performance on a range of mental tasks, including tests of attention.

A separate group of 43 people completed three different tasks of working memory, as well as the same subitizing task as before, the same change-detection task, and also an object-tracking task, which required them to track four target dots as they moved around the centre of a screen, among four other dots.

While working memory capacity did partially explain object-tracking performance, subitizing performance was also important. Also, perceptual capacity (indicated by results on the subitizing task) strongly predicted the participants’ performance on the photograph change-detection task, even when working memory capacity was controlled for.

“Taken together, the results indicate that a single unifying construct appears to underlie subitizing, change detection and [object-tracking] and this construct is distinct from working memory capacity,” the researchers write.

Importantly, they say, the work also establishes the subitizing task as a simple way of quantifying an individual’s general perceptual capacity limit. As such, it provides “a potentially powerful indicator of individual abilities relevant to various tasks” – such as working as a pilot or a baggage screener at an airport. “The present research thus provides a scientific basis for devising future personnel selection tests for security and defense,” Eayrs and Lavie conclude.

—Establishing Individual Differences in Perceptual Capacity

Image via Giphy.com

Emma Young (@EmmaELYoung) is Staff Writer at BPS Research Digest