Mental efforts and fatigue as consequences of monotony
Pavel N. Prudkov
Selskohosyastvennaya street 12-A
Kurzban et al. of the target article associate mental efforts, fatigue with a hypothetical
mechanism able to estimate the utilities of possible actions and select the action with a maximal
utility. However, this approach faces fundamental problems. In my opinion, mental effort and
fatigue are results of a conflict between the monotony of long-term activities and the novelty
In the target article Kurzban et al. attempt to explain such phenomena as mental effort, fatigue,
and boredom. They derive these phenomena from the functioning of a hypothetical mechanism
which mechanically estimates the utilities of different possible actions, and then selects the
action that has a maximal expected utility. The idea seems interesting but its implementation in
the article has fundamental problems. The article contains no formal description of possible
actions. Kurzban et al. arbitrarily select possible actions for each situation considered in the
article. However, such approach is incorrect because the number of possible actions is potentially
infinite in any situation (Russell& Norvig 2003). Because possible actions can be very different
the unconscious comparison of its utilities seems impossible. Kurzban et al. do not explain how
the mind compares doing mental calculations and mind wandering. The functioning of the
hypothetical mechanism is described abstractly without pointing to the situations in which
mental effort and boredom occur (see the target article’s Figure 1). As a result, it is unclear why
the output of this mechanism is mental effort and fatigue rather than, for example, fear and
anxiety. Fear and anxiety can obviously be applied to optimize costs and benefits.
Another model can be sketched as an alternative to Kurzban et al.’ approach and the theories of
depleting resources. Some details should be specified prior to the description of the model.
Mental efforts and fatigue occur in two sorts of situations. First, mental effort and fatigue usually
occur when an individual attempts to acquire novel skills. However, this activity is typically not
perceived as boring and negative. As an individual acquires a novel skill, the feeling of mental
effort usually disappears (Logan 1985). It is reasonable to assume that in this case mental efforts
simply reflect the necessary restructuring of the mind. Second, mental effort and fatigue
frequently occur when the mental activity of an individual is not difficult but long-term. In this
case, mental effort is perceived as aversive. Obviously, the experiments in the target article were
simple but long-term mental activities. The proposed model deals with such situations.
The model is based on two assumptions. First, the mind is able to maintain several processes in
parallel. One of the processes is a task which occupies the focus of consciousness while other
processes function in a background mode. Second, pursuing a long-term goal is usually an
execution of the limited number of actions, many of them should be performed over and over
again. As a result, any long-term activity is a sequence of recurring actions and therefore it is
The brain has two systems which process monotony and its antagonist, novelty. One system is
associated with the hippocampus (Grossberg & Merrill 1992; Vinogradova 2001). The system
has a representation of the ongoing situation and compares it with the input from other brain
systems. The mismatch between the representation and input means that the situation is changed
and then the brain is activated. If the representation matches the input then habituation occurs
and the brain activity is decreased (Vinogradova 2001). The second system is the novelty
seeking system which is responsible for seeking novel and varied sensations and experiences
(Zuckerman 1994; Roberti 2004). The functioning of this system is associated with the
interaction between neurotransmitter systems that are concentrated in the limbic areas of the
brain (Zuckerman 1996).
It can be hypothesized that the monotony of long-term activities leads to the engagement of both
novelty processing systems. The first system attempts to inhibit the ongoing task and the second
system tries to activate any parallel processes. The feeling of mental effort reflects the
competition between the task, which suffers from inhibition, and other processes. Fatigue and
boredom mirror the inhibition of the ongoing task and habituation. The reduction of performance
in such tasks as vigilance tasks results from the inhibition of the task by the first system.
Accordingly, changes in the situation may result in the improvement of performance owing to
the activation of the brain by this system. The decrement in performance when participants
perform sequentially several tasks can be explained on the basis that these tasks share the
common experimental context (one experimenter, one room, etc) and therefore the situation can
be considered monotonous.
The relationship between reward and fatigue can be hypothesized as a consequence of the
interaction between the novelty processing systems and the reward system. Indeed, novelty
seeking should be maximally intense in neutral situations because seeking novel sensations in
very dangerous or very pleasant situations is hardly a useful strategy. As a result, reward can
inhibit the novelty processing systems thus decreasing the feeling of fatigue.
The feelings of fatigue and boredom in long-term activities possibly reflect a conflict between
various brain systems. In my opinion, the ability to pursue long-term goals having no innate
basis is the main characteristic distinguishing humans from other animals (Prudkov 1999, 2005).
The experiments described in the target article are obvious examples of pursuing such goals.
Indeed, subjects participated in the vigilance task not because they were hungry, sexually
unsatisfied, or frightened. The ability is maintained by the prefrontal lobes (Luria 1966, 1982).
This is a young structure maximally advanced in humans (Luria 1966).
However, long-term activities often are monotonous. Monotony results in the activation of the
novelty processing systems. These systems are maintained by ancient limbic structures, which
also maintain other biological goals (Kolb & Whishaw 2002). For the novelty processing
systems, pursuing social goals is a neutral situation because the limbic structures are weakly
involved in processing social goals. Therefore, in this case the novelty processing systems should
be activated thereby hindering social activities.
Kurzban et al. ask ‘why, if revising a manuscript contributes to the achievement of key long-term
goals does it feel aversively effortful?’ (sect. 2.1, para. 4). They attempt to respond to this
question but the target article does not contain a clear answer. The proposed model, however,
offers a simple solution: because a mature scientist frequently revises manuscripts and this
activity becomes monotonous.
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