In their motor-oriented approach to consciousness, Morsella et al. distinguish between conscious and unconscious processes: “Although one is unconscious of these complex programs (Johnson & Haggard Reference Johnson and Haggard2005), one is often aware of their proprioceptive and perceptual consequences” (target article, sect. 3.1, para. 2, emphasis in the original).
I will discuss a case in which perceptual consequences remain hidden despite large changes in sensory stimulation. The situation is the most frequent of all human behaviors, the saccadic (jumping) eye movement that moves visual fixation from one location to another. Saccadic eye movements occupy an intermediate range between actions that are almost always conscious, such as movements of the fingers, and those that are never conscious, such as the smooth-muscle actions of the digestive system. Like breathing, the generation of eye movements can be conscious but normally is not. As a striated muscle system, the movements should be conscious in the context of Morsella et al.'s elemental, action-based, simple, and evolutionary-based (EASE) perspective. Consciousness requires attention to the consequences of an action.
Here the job of the nervous system is not to perceive a large change in stimulation from the receptors, but to prevent such a change from reaching consciousness. All visual information arrives from retinas that encounter a large change in stimulation, a shift of the entire visual world, with every saccade. Normally the change is not perceived, but under some circumstances, it can be perceived (Deubel et al. Reference Deubel, Bridgeman and Schneider1998). If a saccade causes gaze to reach its target, the result is usually space constancy – negatively defined, this means that a jump of the retinal world is not perceived despite the large change in the stimulus. The motor-oriented approach of Morsella et al. links the sensory and motor aspects of a saccade, allowing a reorientation in terms of reafference.
Retinal signals reach the primary visual cortex and beyond in a code that is not space-constant – cortical stimulation shifts with eye movements even though perception does not (Bridgeman Reference Bridgeman1973). Hence, we already know that the content of the primary visual cortex is not conscious. The paradoxical situation arises that the proprioceptive and perceptual consequences of saccades reflect the world, that does not move, and not the retinal image that does move. In fact, there is no visual brain area that shows no change across a saccadic eye movement, because space constancy is in this sense a systematic failure of conscious perception rather than a detection of an external event. Consciousness is directed to the stable world, not to the moving receptors.
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In their motor-oriented approach to consciousness, Morsella et al. distinguish between conscious and unconscious processes: “Although one is unconscious of these complex programs (Johnson & Haggard Reference Johnson and Haggard2005), one is often aware of their proprioceptive and perceptual consequences” (target article, sect. 3.1, para. 2, emphasis in the original).
I will discuss a case in which perceptual consequences remain hidden despite large changes in sensory stimulation. The situation is the most frequent of all human behaviors, the saccadic (jumping) eye movement that moves visual fixation from one location to another. Saccadic eye movements occupy an intermediate range between actions that are almost always conscious, such as movements of the fingers, and those that are never conscious, such as the smooth-muscle actions of the digestive system. Like breathing, the generation of eye movements can be conscious but normally is not. As a striated muscle system, the movements should be conscious in the context of Morsella et al.'s elemental, action-based, simple, and evolutionary-based (EASE) perspective. Consciousness requires attention to the consequences of an action.
Here the job of the nervous system is not to perceive a large change in stimulation from the receptors, but to prevent such a change from reaching consciousness. All visual information arrives from retinas that encounter a large change in stimulation, a shift of the entire visual world, with every saccade. Normally the change is not perceived, but under some circumstances, it can be perceived (Deubel et al. Reference Deubel, Bridgeman and Schneider1998). If a saccade causes gaze to reach its target, the result is usually space constancy – negatively defined, this means that a jump of the retinal world is not perceived despite the large change in the stimulus. The motor-oriented approach of Morsella et al. links the sensory and motor aspects of a saccade, allowing a reorientation in terms of reafference.
Retinal signals reach the primary visual cortex and beyond in a code that is not space-constant – cortical stimulation shifts with eye movements even though perception does not (Bridgeman Reference Bridgeman1973). Hence, we already know that the content of the primary visual cortex is not conscious. The paradoxical situation arises that the proprioceptive and perceptual consequences of saccades reflect the world, that does not move, and not the retinal image that does move. In fact, there is no visual brain area that shows no change across a saccadic eye movement, because space constancy is in this sense a systematic failure of conscious perception rather than a detection of an external event. Consciousness is directed to the stable world, not to the moving receptors.