Visual Binding: An Automatic Process?

Some theories suggest that color and shape information - processed in different parts of the brain - must be integrated by attention in order to give rise to a coherent visual experience (in other words, attention is thought to solve the "binding problem"). Although that explanation is probably not satisfying to many, no doubt mostly because attention itself is an ill-defined construct, at least it's a beginning in solving the binding problem. However, a recent article from Allen, Baddeley & Hitch argues that even this humble claim may be entirely wrong.

Allen et al. suggest that the binding of visual features may actually automatic insofar as it does not share resources with any other cognitive processes. For example, "verbal load" (i.e., repeating the word "Monday" again and again) does not interfere with individual visual short-term capacity limits. Allen et al. reasoned that perhaps other more complex tasks would also not interfere with this ability.

To demonstrate this, they first gave 8 subjects a task in which they had to remember the shape and color of four objects. Afterwards, they were asked to judge whether a single shape, color, or shape-color combination was present in the previous array. Every subject completed 384 such judgments, with negative feedback and instructions to emphasize accuracy rather than speed. In general, subjects were better at color judgments than shape or both-color-and-shape (i.e., binding) judgments. Allen et al. suggest that the similar accuracy between the shape and the binding condition may reflect an automatic process.

In a second experiment, 16 subjects repeated the task from the first experiment, and also repeated it while counting backwards by one from some number presented on the screen. A nearby experimenter monitored their performance on this secondary task. If binding is not automatic, but requires additional cognitive resources, then one would expect backward counting to more strongly affect performance in the binding condition than the other conditions. The results did show that performance was generally lower when subjects had to perform this concurrent task, but that the binding condition was similarly affected by this task as the shape- and color-only conditions. In other words, binding seemed automatic.

Based on this surprising result, the authors thought that maybe backwards counting is not demanding enough resources to show a differential impact on binding processes. To this end, they gave 24 subjects the same task as in the first experiment, except that during each trial of the task they had to remember the serial order of 6 randomized digits, and to recall these numbers correctly after each trial. (In addition, the authors made a modification to the design which included 25% feature repetition trials, because without the possibility of features repeating, memorizing just a single feature combination could result in differential benefits to the binding test, relative to shape- or color-only tests). The results showed that this digit recall test also impacted binding and shape- or color-only conditions equally, again suggesting that the maintenance of combined visual features is no more demanding than the maintenance of the features themselves.

However, the authors worried it could still be possible that binding is not automatic but rather that the digit recall task was simply not demanding enough. To this end they gave another 24 subjects the same task as in experiment 1, except for some trials subjects had to count backwards by 3s from a given number while performing the task. Their performance on the backward counting task was monitored. As before, this concurrent counting task generally decreased performance, but this was not more true of binding than the color- or shape-only conditions. In other words, binding still appeared to be automatic!

Contrary to these results, previous work has shown that binding is very fragile in one particular scenario: if subjects are presented with multiple objects during the judgment rather than a single item. Allen et al. reasoned that if this is the case, then sequential presentation of each item during the memorization period might decrease performance on binding more than in the shape- or color-only conditions. To test this, Allen et al. gave 36 subjects the same task as in the first experiment, except that items were presented sequentially during encoding and a simple articulatory suppression task was given (i.e., the "verbal load" mentioned at the start of this post, in which subjects merely repeat a simple phrase again and again). This manipulation did affect binding differentially, such that the decrease in performance resulting from sequential presentation was much greater in the binding condition than in the shape- or color-only conditions. This demonstrates clearly that binding is not invincible - but it does not appear to require the same form of attention as digit span or backwards counting.

So, it looks like binding is automatic, insofar as it is not affected by other simultaneous tasks. On the other hand, perhaps the authors didn't run enough subjects to show a statistically significant effect. To test this, the authors combined the results from the first four experiments using meta-analytic methods, and confirmed that even after pooling all the results, there were no differential effects of concurrent tasks on the binding condition.

The authors conclude that these results support the idea that a separate "binding process" can often proceed automatically and does not appear to share resources with those involved in many secondary tasks. The authors do suggest that some forms of binding may require more active, effortful processing, such as those involving longer encoding intervals. These results are a humbling demonstration that the "binding problem" - a problem that has stumped many cognitive neuroscientists - is solved nearly effortlessly by the human brain.

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I thought awhile about this...and i can't help but be reminded of chunking effect. Perhaps the items have been stored as chunks within working memory, and that chunking is automatic due to memory strategies. This chunking effect could account partially for the differences between experiments that presented single versus multiple items during judgement tests. This might be caused by the proposed chunk recall limits (where 1 chunk recall would be easier compared to several chunks at the same time).

The differences between the colour versus shape and binding judgements might be caused by the distinctiveness effect. Distinctiveness could probably be measured with the concreteness of colour versus the concreteness of a shape or shape-colour item. When compared, colour is much more distinctive feature used during commonplace communication. Colours are mostly used as reference points for buildings and other items, whereas shapes as used on a secondary basis where the shape has to be awkward to be placed with higher priority. Using this analogy, one could say that colour would be held in higher priority compared to shape, because i do believe that shapes used would be the commonplace shapes that are seen on a daily basis. While the shape-colour (binding item) would have similar value as the shape because colour still holds higher priority. However, with this analogy it is debatable whether there is more priority between shape of the binding item.

Thogh, by using that analogy and combining it with the chunking effect paradigm. In my opinion, i think it might be a good measure ask participants to identify whether the colour was present and after that what shape it was associated with. Perhaps, if there was high similarity of correct answers for identifying colour and the associated shape as well, it could also serve as proof that visual binding is an automatic process (because in this case, visual binding could be considered a strategy used by the mind when chunking information).

What do you think?

Chunking is usually considered an effortful process when done on the fly - involving the "central executive" in Baddeley's terms. But given this demonstration that binding appears automatic, maybe chunking is too? who knows.

There are some cases where this kind of "chunking" would clearly be automatic, and make the task easier. For example, the inclusion of a red heart or a yellow circle (i.e., like the sun) would probably make the task significantly easier, since those combinations are well practiced/known.

I really like your proposal to ask subjects which shape a given color was connected with. I am preparing to begin a research study on binding and we considered doing exactly that - in order to learn what kind of mistakes people are making.

By Chris Chatham (not verified) on 27 Mar 2007 #permalink

Wow that's cool! I hope to be designing experiments too! =)

About chunking: I believe that there's a transition between erm...intentional process to automatic process. I'm not too sure if i got the intentional processing term correct, but i know that an automatic process makes tasks almost effortless.

If the "effort" in Baddeley's construct was the "amount of attention" required, then it can be an automatic process would require negligible amount of effort. I think that because of the memory strategies that participants use, the chunking effect would vary. I've read in several cognitive psychology researches on the chunking effect, that they have tried to manipulate how the participants "code" their items. For example, coding would be using the different control processes (e.g. visual imagery, repetition, or elaboration...). In these cases, researchers would expose participants to lessons on using the specific strategies, which would act as control processes for memory storage. This would be manipulation of their coding strategies, however there would not be 100% assurance that participants would use the taught strategies. That assumption was seen as an acceptable flaw in their research.

However, in other researches, i've also seen participants told that which items in the tasks are more important. Like, they would instruct the participants to do a tasks, and also inform them that they would be tested for item a, b or c later on in the experiment. I think in testing for visual binding this method would be more appropriate (that is if you're equating binding to "automatic chunking"). But in visual binding, i think it would be better to use two items that are unrelated (e.g. unrelated colour with shape), because it would become more of a test of chunking if familiar items were used. In my opinion, from what i've read through the post, i think that automatic chunking of familiar items is just a part of visual binding. I think visual binding would have to be equated to the sum of attentional requirements for automatic chunking and effortful chunking, for a more accurate conceptualization.

I think it something like this:
visual binding = connecting two items together for recall later but through indirect memory functions (because you're testing for a automatic process)

chunking effect, because of individual strategies is also an indirect memory function (the strategies are functions being used directly and we may consciously try and remember two items together, but we do not consciously "chunk" them together. I think chunking would be the underlying function that connects them together into a stronger string. But, we have certain degree of control to how we can manipulate the chunking of items. But not all items that we chunk together are what we intended to, sometimes they just seem to come together. That's what made me come to the conclusion that there is such as "automatic chunking" and "effortful chunking", which you pointed out from Baddeley's discription of the central executive.)

Due to the similarities that chunking and visual binding share, i think that they can be equated together as plausible measures for each other, or perhaps correlated items.

Perhaps your experimental findings for what mistakes people are actually doing, might be caused by a familarity effect (automatic chunks overwriting effortful chunks). Because it has been shown by research i believe, that people tend to "fill in" for non-existant items naturally with things that "make sense to them". I read about this many years back on national geographic magazine i believe. Maybe when participants have binded items that are only partially intact, then will be more likely to fill in the missing one with an item that is more suitable to fit with the other item in that binding pair.

It's all so interesting to me. I'd seriously like to explore more about the dynamics of how people relate items together. Those are my opinions from what little knowledge i have on chunking and binding. There's just so much to find out! ^^