I have just returned from the annual Vision Sciences Society meeting and saw some really fascinating presentations. Over the next couple weeks, I’ll feature a few of them. The first one addresses the consequences of being ignored (if you are a colored shape, that is).
One of this year’s more intriguing presentations, at least for me, came on the first night’s poster session. My former graduate student and now superstar prof. at the University of Delaware, Steve Most, showed that what you ignore at one time can affect what you notice later. He combined two traditionally distinct tasks, negative priming and inattentional blindness. In a typical negative priming study, people might view two overlapping shapes of different colors, but focus on just one of them to make some judgment about it. When you selectively focus on just one of the shapes, you actively inhibit or ignore the other shape, and doing so has consequences. For example, if the shape you ignored later becomes a target shape that requires a response, you will be a little slower to respond. Typically, your response to the previously ignored shape would be slowed by 10-20 milliseconds relative to your speed if you had not ignored it. It’s a small effect that emerges when you average across many trials.
In contrast, Inattentional Blindness studies typically use a single critical trial in which an object appears unexpectedly while people are focusing on something else. The central finding is that people often fail to notice dramatic and obvious stimuli (e.g., chest-thumping gorillas) when their attention is focused on some other aspect of the display and they don’t know it’s coming. (See The Invisible Gorilla for a lot more discussion.)
Most and his colleagues combined these two tasks in an original way to ask an intriguing question: If people ignore a shape or color repeatedly, will they be less likely to notice it when it appears unexpectedly in a different task? That is, does ignoring a color have a lasting effect on what we see, affecting not just how fast we process it later, but whether we see it at all?
Each trial in the study had a sequence of tasks. First, subjects viewed a cross and had to judge whether the horizontal or vertical line was longer. Then, they saw one green digit and one red digit and immediately afterward they were shown a color and had to report the corresponding digit. Only after doing this sequence of tasks 48 times did the experience the critical trial. This time, when the cross appeared, either a green or red shape unexpectedly appeared along with it. The question is whether the color they had been asked to report on the immediately prior trial influenced noticing of the unexpected shape. For example, on trial 48 they might have been asked to report the red digit. Then, on trial 49, a green shape appeared alongside the cross. The question would be whether having focused on red and ignored green on the preceding trial would make people less likely to notice an unexpected green shape.
The core finding: when people had just been asked to report the green digit and the shape was green, 72% noticed the shape. But, when asked to report the red digit and the shape was green, only 44% noticed. In other words, ignoring the green digit led people to miss the green unexpected shape. Setting your attention to ignore green things inhibits noticing of other green things, even those you don’t know are there.
What is most remarkable about this result is that the inhibition from a negative priming task had such a large effect on noticing of something unexpected. Negative priming effects tend to be small delays in how long it takes to process something, not large effects on whether or not you see it. what is unclear is whether you actually need 48 trials of practice to produce this sort of effect. If not, then be careful what you choose to ignore — it might keep you from noticing something important later.
update: corrected the description of the colors of the digits and shapes.
Most, S. B., Kuvaldina, M., Dobson, K., & Kennedy, B. L. (2011, May). Prior perceptual decisions drive subsequent perceptual experience: Negative priming increases inattentional blindness. Poster presented at the annual meeting of the Vision Sciences Society. Naples, FL. http://www.visionsciences.org/abstract_detail.php?id=16.522