“Visual search and dual tasks reveal two distinct attentional resources.”

What are serial processing and parallel processing in attention?

I don’t know how familiar people born after the 1980s would be with it, but some time ago the “Where’s Wally?” series of picture books was very popular. You know, the ones where you have to look for Wally (known as “Waldo” in US and Canadian editions) in pictures that are teeming with people.

Reference URL for the above picture

Unless they are remarkably talented, I doubt that anyone can pick him out at a glance. Most people probably search for him by moving their gaze in a pattern from right to left, from top to bottom (or the other way around). Given this, Wally could be considered a difficult visual target that you have to search for in order. I think that this could be different depending on the time and situation. If the picture were of Wally swimming in a tank in an aquarium with the fish, he would be easy to find. This kind of information processing—to find something that you can see with a glance, such as finding red in a sea of black—is called parallel processing. This is because you can process black and red together in parallel and distinguish them quickly.

By contrast, when you have to look for Wally in a town scene, you process the information permutatively, in order. I believe that this kind of attention can be called parallel processing-type attention.

When looking for something, you can sometimes look and find it straight away, but other times you need to look carefully in order. But this is not always the case. If Wally, who you usually need to look methodically for, were depicted all alone in the middle of the desert, he would be found immediately. There are also ones like Swimmy, the black fish who stands out among the other red fish, but if Swimmy was among a school of black fish, you would not be able to find it without looking your hardest.

In this way, whether the visual target is comparatively complex or comparatively simple, you will be able to find it by parallel processing in some cases and by serial processing in other cases, depending on the situation.

The paper I discuss today investigates these things. The model proposed in the paper could be depicted as follows.

Using this diagram, we should be able to understand that the type of processing changes according to the combination of the target and situation, so that simple attention tasks such as searching for red will use parallel processing or serial processing, depending on the case, and searching for a man wearing a striped shirt and glasses may be difficult (parallel processing) or easy (serial processing).

[Abstract]

Most theories of visual processing assume that a target will "pop out" from an array of distractors ("parallel" visual search, e.g., color or orientation discrimination) if targets and distractors can be discriminated without attention. When the discrimination requires attention (e.g., rotated L vs. T or red-green vs. green-red bisected disks), "serial" examination is needed in visual search. Attentional requirements are also frequently assessed by measuring interference from a concurrently performed attentionally demanding task. It is commonly believed that attention acts equivalently in dual-task and visual search paradigms, based on the implicit assumption that visual attentional requirements can be defined along a single dimension. Here we show that there is no such equivalence: We report on targets that do not trigger pop-out, even though they can be discriminated from distractors with attention occupied elsewhere (natural scenes, color-orientation conjunctions); conversely, we show that certain targets that pop out among distractors need undivided attention to be effectively discriminated from distractors when presented in isolation (rotated L vs. T, depth-rotated cubes). In other words, visual search and dual-task performance reveal attentional resources along two independent dimensions. We suggest an interpretation of these results in terms of neuronal selectivities and receptive field size effects.

Reference UTL: Visual search and dual tasks reveal two distinct attentional resources.

Comments

When I was looking for information about the Where’s Wally series, I also found a very scary video based on these characters. Be sure not to look at them if you are weak of heart.

This sort of thing can probably be explained from the relationship between the attention function and the amygdala, but it was so, so scary.