Developing Intelligence

Given a fixed amount of computational power in designing an intelligent system, there is a necessary tradeoff between how many resources are devoted solely to the current task, and how many resources are devoted to monitoring for information that may be important but is not necessarily relevant to the current task. If more resources are dedicated to the current task, it may be accomplished more quickly – but at the same time, this setting may make it more difficult to reorient and switch to a different task. On the other hand, if more resources are dedicated to monitoring or reorienting, then the current task may not be completed as accurately or quickly.

This tradeoff is a form of the “stability-flexibility dilemma” – much recent research in cognitive neuroscience has focused on how the stability-flexibility dilemma is managed by the brain. One theory is that an inhibitory process “kicks in” to help switch to a new task by actively suppressing the representations relevant to the old task. Consistent with this account, some work has shown that people are slower to switch to task A if they have performed it more recently relative to having performed it slightly longer ago (at least, within the context of a laboratory task-switching paradigm where task switch as follows ABACBACABCAB etc.) This is known as a “set alternation” or “backwards inhibition” cost, and is thought to reflect the residual inhibition of task A, even though subjects should now be activating it, rather than inhibiting it.

On the other hand, set-alternation costs might also reflect less efficient processing if the two instances of task A require different responses: in this case, it is not inhibition of A, but rather the particular stimulus-response mapping used on task A that is interfering with performance on the current trial, which may contain a different stimulus. To rule out this explanation, Ulrich Mayr performed an experiment in which the effects of repeating tasks, stimuli, and responses could all be dissociated.

If the mismatching stimulus-response mappings were to blame for set-alternation costs, subjects should not show set-alternation costs on a task where the neither the stimulus nor the response was repeated relative to the last time that task was completed. The results showed that when switching tasks, subjects were slower when switching to a more-recently performed task than to a less-recently performed task (the set-alternation cost). There was less slowing if people were given longer until the instructions of the next trial, but there was not less slowing if people were given longer after the instructions for the next trial. This result is consistent with previous work by the same author, and is interpreted to reflect that the inhibition of the previous task cannot be reduced through preparatory processing (and thus may not be under conscious control).

Importantly, the set-alternation cost also was not affected by whether the response repeated relative to the previous trial. In other words, people were slower to switch to a more recently performed task relative to a less recently performed task, even if everything about that task was the same as when they had last performed it. This result contradicts the theory that set-alternation costs are actually caused by mismatching stimulus-response mappings from previous iterations of the task.

Mayr argues that this supports the idea of inhibition as an enabling factor in the flexibility-stability dilemma in task-switching paradigms, but this argument portrays inhibition in a very strange light: it appears to be an uncontrollable process. It is therefore hard to understand how this automatic and un-overrideable process can be an agent of “high level control.”

Furthermore, some recent evidence suggests that task-switching is associated with a slowing of RTs not only because stimulus-response mappings must change (this is the theoretically interesting aspect of task-switches) but also because you are providing them with a cue that the task may have changed; it takes time to process that. Accordingly, I haven’t seen a replication of the backwards inhibition cost when controlling for the effects of cue switches.

In the end, however, Mayr has presented interesting evidence in favor of one theory about the stability-flexibility dilemma. There are reasons to think that the putative inhibition in this task is not the same as other forms of inhibition (as in Stroop or Stop Signal), primarily in that this appears to be an involuntary form of inhibition.

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  1. #1 Anson
    June 14, 2007

    Though differences in cue do seem to at least partially account for longer RTs when switching, it doesn’t make sense to me that they could account for longer RTs when returning to a recently abandoned task set. The reason being that the cue is the same as from before, so without an inhibition account, then the repetition of a cue should actually speed up responses instead of slow them down. If you thought that the inhibition is happening to the representation of the cue and that is why more time is needed to use that cue than you could be onto something. but than again there is some research stating that inhibition doesn’t not happen until presentation of the stimulus (not during the cue).
    Which in turn does suggest that the inhibition captured in this paradigm is “local inhibition”, in which the most active representation laterally and automatically inhibits competing representations.
    the reason that it can still be construed as being an “agent of higher level control” is because the local inhibition may be happening in working memory to control working memory representations. I think part of the confusion is due to the assumption that the mechanisms of higher order thought have to be conscious and intentional. However, it often seems that we only become conscious of something or aware of an intention after the fact (libet studies, etc). So it is seems to me quite likely that there may be quite a few unconscious and unintentional mechanisms involved in generating and maintaining higher order thought.

  2. #2 CHCH
    June 15, 2007

    Hi Anson – Thanks for commenting!

    [Without inhibition] “the repetition of a cue should actually speed up responses instead of slow them down”

    Maybe – or maybe cue repetition has greater benefit when it’s been slightly longer since the cue was last used. PDP has an “accomodation current” based on calcium ion flux that models a similar kind of thing. To be fair, I am stretching here – Ca++ concentrations may vary over a different time frame than what we’re talking about, and I don’t know.

    But to address your larger point about local inhibition as an agent of higher level thought, I agree that mechanisms *important* for E.F.’s (etc) need not be conscious or intentional (just as potassium currents are important for them), but I wouldn’t call something as automatic and universal as lateral inhibition an *agent* of higher level thought. For example, you get more local inhibition when you more highly activate another competing representation – in this way it is a byproduct of another process. Thus lateral inhibition seems to be secondary to the ability to activate a new representation, and *that* may be variable that would show important individual differences. But I think I’m repeating myself now from earlier arguments!

    I’m happy you stopped by to challenge me on this point – I do think you’re right that the cue-switch issue doesn’t really explain backwards inhibition w/o recourse to inhibition.

    Anson, have you ever looked at the relationship of “no-go learning” (as distinct from “go” learning) to other measures of inhibition? I wonder whether there would be a relationship.

  3. #3 Jim Grange
    March 27, 2009

    Very interesting comments. Regarding the presence of Backward Inhibition (BI) when controlling for cue switches has since been addressed by Erik Altmann (2007: JEP:LMC, 33, 892-899), and seems to be equivalent if cue switches for ‘A’ across an ABA sequence.

    Regarding the comments about BI targeting response stages, our lab has just published some work that suggests inhibition can be found during task preparation processes when response processes are controlled for. I refer you to my website for the articles if you are interested, (Grange & Houghton, 2009; Houghton, Pritchard, & Grange, 2009).

    I realise these comments are rather tardy in response to the original postings, but maybe some will find it of interest!


    Jim Grange.
    Bangor University.

  4. #4 Ion Juvina
    November 9, 2010

    I also found Backward Inhibition in Stroop when looking at sequence (between-trial) effects. See the paper (including a computational model) here:

    ~ Ion Juvina
    Carnegie Mellon University

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