In the target article, authors Morsella et al. claim that consciousness functions to integrate “incompatible skeletal muscle intentions for adaptive action” (sect. 2.4, para. 5). The authors' claim is one of necessity: “[T]he conscious field is necessary to integrate what appear to be multiple inclinations toward the skeletomotor output system” (sect. 2.4, para. 5; emphasis mine). In this commentary, I identify a worry – namely, that the authors have not adequately defended the strong necessity claim. Necessity claims are inherently vulnerable: a single counter-example renders the claim false. I suggest that there is both prima facie reason to think that skeletomotor integration can occur unconsciously, and some positive empirical evidence that it can.
The authors note that many theories of consciousness specify the purpose of consciousness to be quite high level – for example, the maintenance of the self, semantic processing, or theory mind. In contrast, the authors think consciousness serves a “counterintuitive, passive, and ‘low level’” function (target article, introductory para. 1). A risk of identifying the function of consciousness to be low-level is that it will turn out that the low-level task can be subserved by non-conscious processes. The more basic the role granted to consciousness is, the more likely that scientific investigation will reveal that the function can be achieved in the absence of consciousness.
To support the claim that consciousness is necessary for skeletomotor integration, the authors must convincingly argue that there are no cases of unconscious skeletomotor integration. Contrasting cases of obviously conscious integration like holding one's breath underwater with cases of unconscious (non-skeletomotor) integration like the McGurk effect is too weak a method to support the necessity claim. How do we know that there are not cases of unconscious skeletomotor integration of which we are not aware, given that such integration would be unconscious?
The authors do not give a precise definition of “integration,” but they do give useful examples. Holding one's breath underwater requires integration. In this case, a reflexive action (inhaling) is inhibited by one's goals (wanting to survive). Action inhibition appears therefore to count as integration. If there are cases of unconscious action inhibition, then this would presumably mean there are cases of unconscious integration.
There is prima facie reason to think the relevant integration/conflict can occur unconsciously. The authors claim that conscious conflict occurs whenever there are multiple incompatible inclinations on skeletomuscles. On a weak reading of “inclinations,” in which an inclination is simply an activated motor plan, the phenomenon of “incompatible skeletal muscle intentions” (sect. 2.4, para. 5) is not particularly rare. Motor plans are automatically activated to a wide range of stimuli, a point the authors acknowledge: “[There is] overwhelming evidence demonstrating that the presentation of action-related perceptual stimuli automatically and systematically influences action processing” (sect. 3.2, para. 3). Simply viewing or categorizing an object primes motor responses associated with the object, like grasping actions (Tucker & Ellis Reference Tucker and Ellis2004). These motor responses are clearly often incompatible with current goals: grasping reflexively at a stranger's personal effects would be quite deleterious, for instance. If motor plans are indeed activated as ubiquitously as the research suggests, then it is likely that incompatible actions – or even, “unconscious urges” – are activated and suppressed beneath conscious awareness all of the time. Perhaps the authors would counter that these incompatible inclinations are all conscious. However, it does not seem as if we are constantly bombarded with conscious urges to grasp the objects we encounter. The authors might also contend that action inhibition is not integration. But the primary examples of conscious integration that the authors offer, such as holding one's breath underwater, are cases in which a reflexive action is inhibited.
Consistent with the claim that the brain is constantly engaged in the suppression of unwanted incompatible motor plans, consider the effects of releasing these inhibitions. Under the influence of alcohol or other inhibition-releasing drugs, people behave quite differently – they are more aggressive, for example, and find themselves making inappropriate or irreverent comments. Although it often seems like the alcohol “created” or “implanted” these inclinations, it is plausible that they are present even while sober; however, because unconscious inhibitory mechanisms are in place to suppress them, they are not consciously experienced. Consider that we often find ourselves acting appropriately and in-context without any effort at all, such as when we are able to remain quiet at a movie or show. At first, one might accidentally talk at inappropriate times, but eventually, remaining quiet becomes less effortful or entirely un-effortful. This does not demonstrate that it is definitely the result of unconscious inhibition. But how do we know that it is not? The authors claim that there are no cases of this unconscious integration. If there is reason to think there might be unconscious integration, then the authors must explain why this is mistaken.
In addition to the concerns I have raised, there is positive empirical evidence that actions can be suppressed unconsciously. One widely discussed finding that is taken by many to evince unconscious inhibition is the negative compatibility effect. The negative compatibility effect refers to the ability of subliminal action-suggesting primes (such as a leftward arrow priming a left response) to render performance worse when a congruent or compatible response must be made to a target, under certain conditions. For instance, if a prime such as “>>” is subliminally presented prior to a target (“>>”) and there is a significant delay between prime and target, responses to congruent targets is slower than incongruent targets (Eimer & Schlaghecken Reference Eimer and Schlaghecken2003; Schlaghecken et al. Reference Schlaghecken, Bowman and Eimer2006). (The effect reverses with a shorter prime–target delay.) A standard explanation for the effect is that it involves an unconscious inhibitory mechanism that suppresses the activated motor response from the prime, in order to preempt interference from the prime on the response to the target (Jaskowski & Przekoracka-Krawczyk Reference Jaśkowski and Przekoracka-Krawczyk2005; Schlaghecken & Eimer Reference Schlaghecken and Eimer2006; Sumner et al. Reference Sumner, Nachev, Morris, Peters, Jackson, Kennard and Husain2007). This occurs entirely beneath subjects' awareness because the subjects are never aware of the prime. The negative compatibility effect therefore provides some positive evidence that consciousness is not required for skeletomotor integration.
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In the target article, authors Morsella et al. claim that consciousness functions to integrate “incompatible skeletal muscle intentions for adaptive action” (sect. 2.4, para. 5). The authors' claim is one of necessity: “[T]he conscious field is necessary to integrate what appear to be multiple inclinations toward the skeletomotor output system” (sect. 2.4, para. 5; emphasis mine). In this commentary, I identify a worry – namely, that the authors have not adequately defended the strong necessity claim. Necessity claims are inherently vulnerable: a single counter-example renders the claim false. I suggest that there is both prima facie reason to think that skeletomotor integration can occur unconsciously, and some positive empirical evidence that it can.
The authors note that many theories of consciousness specify the purpose of consciousness to be quite high level – for example, the maintenance of the self, semantic processing, or theory mind. In contrast, the authors think consciousness serves a “counterintuitive, passive, and ‘low level’” function (target article, introductory para. 1). A risk of identifying the function of consciousness to be low-level is that it will turn out that the low-level task can be subserved by non-conscious processes. The more basic the role granted to consciousness is, the more likely that scientific investigation will reveal that the function can be achieved in the absence of consciousness.
To support the claim that consciousness is necessary for skeletomotor integration, the authors must convincingly argue that there are no cases of unconscious skeletomotor integration. Contrasting cases of obviously conscious integration like holding one's breath underwater with cases of unconscious (non-skeletomotor) integration like the McGurk effect is too weak a method to support the necessity claim. How do we know that there are not cases of unconscious skeletomotor integration of which we are not aware, given that such integration would be unconscious?
The authors do not give a precise definition of “integration,” but they do give useful examples. Holding one's breath underwater requires integration. In this case, a reflexive action (inhaling) is inhibited by one's goals (wanting to survive). Action inhibition appears therefore to count as integration. If there are cases of unconscious action inhibition, then this would presumably mean there are cases of unconscious integration.
There is prima facie reason to think the relevant integration/conflict can occur unconsciously. The authors claim that conscious conflict occurs whenever there are multiple incompatible inclinations on skeletomuscles. On a weak reading of “inclinations,” in which an inclination is simply an activated motor plan, the phenomenon of “incompatible skeletal muscle intentions” (sect. 2.4, para. 5) is not particularly rare. Motor plans are automatically activated to a wide range of stimuli, a point the authors acknowledge: “[There is] overwhelming evidence demonstrating that the presentation of action-related perceptual stimuli automatically and systematically influences action processing” (sect. 3.2, para. 3). Simply viewing or categorizing an object primes motor responses associated with the object, like grasping actions (Tucker & Ellis Reference Tucker and Ellis2004). These motor responses are clearly often incompatible with current goals: grasping reflexively at a stranger's personal effects would be quite deleterious, for instance. If motor plans are indeed activated as ubiquitously as the research suggests, then it is likely that incompatible actions – or even, “unconscious urges” – are activated and suppressed beneath conscious awareness all of the time. Perhaps the authors would counter that these incompatible inclinations are all conscious. However, it does not seem as if we are constantly bombarded with conscious urges to grasp the objects we encounter. The authors might also contend that action inhibition is not integration. But the primary examples of conscious integration that the authors offer, such as holding one's breath underwater, are cases in which a reflexive action is inhibited.
Consistent with the claim that the brain is constantly engaged in the suppression of unwanted incompatible motor plans, consider the effects of releasing these inhibitions. Under the influence of alcohol or other inhibition-releasing drugs, people behave quite differently – they are more aggressive, for example, and find themselves making inappropriate or irreverent comments. Although it often seems like the alcohol “created” or “implanted” these inclinations, it is plausible that they are present even while sober; however, because unconscious inhibitory mechanisms are in place to suppress them, they are not consciously experienced. Consider that we often find ourselves acting appropriately and in-context without any effort at all, such as when we are able to remain quiet at a movie or show. At first, one might accidentally talk at inappropriate times, but eventually, remaining quiet becomes less effortful or entirely un-effortful. This does not demonstrate that it is definitely the result of unconscious inhibition. But how do we know that it is not? The authors claim that there are no cases of this unconscious integration. If there is reason to think there might be unconscious integration, then the authors must explain why this is mistaken.
In addition to the concerns I have raised, there is positive empirical evidence that actions can be suppressed unconsciously. One widely discussed finding that is taken by many to evince unconscious inhibition is the negative compatibility effect. The negative compatibility effect refers to the ability of subliminal action-suggesting primes (such as a leftward arrow priming a left response) to render performance worse when a congruent or compatible response must be made to a target, under certain conditions. For instance, if a prime such as “>>” is subliminally presented prior to a target (“>>”) and there is a significant delay between prime and target, responses to congruent targets is slower than incongruent targets (Eimer & Schlaghecken Reference Eimer and Schlaghecken2003; Schlaghecken et al. Reference Schlaghecken, Bowman and Eimer2006). (The effect reverses with a shorter prime–target delay.) A standard explanation for the effect is that it involves an unconscious inhibitory mechanism that suppresses the activated motor response from the prime, in order to preempt interference from the prime on the response to the target (Jaskowski & Przekoracka-Krawczyk Reference Jaśkowski and Przekoracka-Krawczyk2005; Schlaghecken & Eimer Reference Schlaghecken and Eimer2006; Sumner et al. Reference Sumner, Nachev, Morris, Peters, Jackson, Kennard and Husain2007). This occurs entirely beneath subjects' awareness because the subjects are never aware of the prime. The negative compatibility effect therefore provides some positive evidence that consciousness is not required for skeletomotor integration.