The argument from which Kurzban et al. set out in their theoretical discussion is that resource scarcity does not satisfactorily explain two well-known phenomena: (1) Performance of volitionally selected tasks often feels like it requires mental effort. (2) That feeling is aversive.

I concur. Subjective effort may have nothing to do with the amount of processing resources expended on an executed task (and it is, furthermore, yet unclear to what extent, if at all, variance in task performance is due to the amount of available resources, since it may as well be due to cross-talk or some other sort of outcome conflict; see Hirst & Kalmar Reference Hirst and Kalmar1987; Navon Reference Navon1984; Navon & Miller Reference Navon and Miller1987). In my view, effort is the typical corollary of attentional selection per se: “Effort is not any scarce commodity. It is the aversive valence of the operation of decoupling. The more sustained decoupling is, the more aversive it is” (Navon Reference Navon1989, p. 203).

The term decoupling denotes an inhibitory operation (mediated by selectively attenuating some communication channels) meant for attaining effective attentional emphasis sufficient for withstanding distractions. That operation seems useful for actuating any task that is not habitual enough to benefit from being served by a dedicated, special-purpose communication channel, and hence must resort to gaining temporary high visibility, subjectively felt as awareness, within an internal communication network accessible by numerous processing modules (for more detail, cf. Navon Reference Navon1989, pp. 200–201).

Furthermore, as stated in Navon (Reference Navon1989): “because effort is aversive, motivation is needed to override the aversion” (p. 203). Therefore, to the extent that aversion is functional, the function of aversion may be to set a high enough hurdle that would most often select for focal attention the best-fitting candidate – that task which the subject is at the time most motivated for. Tasks for which the subject is only mildly motivated are unlikely to be selected, as motivation in this case would often not outweigh effort aversion. Further on, a selected task whose momentary appeal has decreased with time may not be maintained in focal attention, or at least may be less immune to distraction, once the motivation does not suffice anymore to outweigh the aversiveness of effort.

Aversiveness is a particularly good guide, because it is a sort of sentience. Just like the effect of suffering muscle aches on the determination of a marathon runner to keep running must be greater than whatever effect the mere cognitive feedback about physiological measures could have, the felt aversion to keeping the execution of a mental assignment must predict persistence more than would a mental act of merely deliberating how the time could have been alternatively spent.

So far, I suppose, my stance does not appear significantly discordant with the thesis proposed in the target article. Yet, I do have some reservations about the notion that aversion is borne by computing opportunity costs.

Though people clearly prefer to engage in rewarding activities, it seems a bit hard to believe that our information-processing system as a rule manages to gauge and rank on-line, albeit implicitly, the costs/benefits of all alternatives (or even only the most salient ones) sufficiently for estimating opportunity costs. Is it a closed set at all? How large, for example, is the set of all alternatives for what I am doing right now to generate this written sentence?

Furthermore, some of the most powerful triggers of distraction, that naturally require much effort to withstand, are transient stimuli or associations that, in spite of their high capturing potential, would not much benefit a subject's functioning in the short run or well-being in the longer run. To illustrate, my concentration over conceiving and phrasing this sentence would clearly have been much harmed if a flying bird presently had found its way into my office, worse yet if some obsessive image or thought had popped up in my mind. I doubt that I would have been as much distracted by a potential reflection about the next-best objective that I could have otherwise engaged myself with. In passing, is it just incidental that I am now failing to find anything like that in my short term memory (STM)?

Hence, it seems debatable that effort aversiveness is nothing but the felt output of the computation of opportunity costs. Anyhow, that sort of aversion need not reflect opportunity cost to be functional. If its inherent function is to constitute a hurdle high enough for selecting the task that the subject is most motivated for (and later, for maintaining focused attention there), aversion could simply be the experienced output of the extent of decoupling required for doing that.

Finally, performance may deteriorate with time neither because processing resources deplete, as often believed (e.g., Gailliot & Baumeister Reference Gailliot and Baumeister2007), nor because the priority of the attended-to task somewhat declines, as Kurzban et al. suggest. Possibly, the effectiveness of the inhibitory operation termed “decoupling” here, may tend to slowly decay for some reason. Alternatively, the products of pre-attentive processing of unattended objects, perhaps occasionally exercising some failed attempts to invoke attention to themselves, pile up over time in some push-down stack which might bear a gradual increase of outcome conflict, in turn causing distractions to become progressively harder and harder to withstand. To date, there seems to be no sufficient evidence to substantiate any one of these conjectures.