A faint tap per se is not an interesting sound; it may well escape being discriminated from the general rumor of the world. But when it is a signal, as that of a lover on the window-pane, it will hardly go unperceived. William James, 1890 [p. 418]
There’s such a blizzard of sensory information out there, the brain would be overwhelmed if it weren’t for a spotlight process of selective attention that allows us to focus. This means that once we’re tuned into certain aspects of the environment, we’re left blind to events outside of our selective attention – a phenomenon called “inattentional blindness“.
Related to this is the idea of attention as a finite resource. It’s partly because our processing powers are depleted by the focus of our attention that we’re left blind to that which we ignore. A new study builds on the finite resource element of this story. Baruch Eitam and his colleagues propose that pure irrelevance is enough to render information invisible even if we have plenty of resources available for processing that information. It brings a new spin to our understanding of “induced blindness” that’s not just about attentional load but also about salience and motivation.
The researchers presented 100 participants with a central coloured ring surrounded by a larger ring of a different colour. The rings appeared for half a second and were close enough together that they both fell on the high-acuity foveal region of the eye. Before the rings appeared the participants were first instructed to concentrate on either the inner or outer ring. After the rings disappeared, half a second passed and then they were asked to identify which of three distinct colours either the inner or outer ring had been. That is, they were either quizzed about the ring they’d concentrated on or the other one.
As you might expect, the participants achieved nearly perfect performance when identifying the colour of the ring they’d concentrated on (the error rate was just 3 per cent; not significantly different from flawless accuracy). In contrast, they were wrong 25 per cent of the time when trying to identify the colour of the “irrelevant” ring they’d ignored – this is almost seven times the error rate compared with the “relevant” ring. Participants were also less confident in their knowledge about the irrelevant ring.
A follow-up study confirmed that blindness to the ignored ring colour was induced purely by its irrelevance, not because of limitations in attentional resources. Twenty-six participants performed an identical task to before except this time they were instructed to concentrate on both coloured rings. Regardless of which ring they were subsequently quizzed on, their performance was virtually flawless (the error rate was 8 per cent: not significantly different from performance for the relevant ring in the first experiment).
Eitam and his colleagues said their research suggests there are two kinds of induced blindness – the first involves the unavailability of processing resources and is accompanied by a lack of visual awareness, so the missed information is literally not seen. The second, demonstrated here, is based on irrelevance alone and is related to not having sufficiently processed information that was seen.
“We propose that in our study the participants who failed to report the irrelevant colour were aware of it when it was displayed,” the researchers explained, “but due to irrelevance, its abstract representation (of ‘red’ for example) was insufficiently activated, or possibly suppressed, and the participants could not report it.” This an interesting extension of established psychological theory that will surely be of interest to road safety researchers, advertisers and magicians.
Eitam, B., Yeshurun, Y., and Hassan, K. (2013). Blinded by irrelevance: Pure irrelevance induced “blindness”. Journal of Experimental Psychology: Human Perception and Performance, 39 (3), 611-615 DOI: 10.1037/a0032269