Blindsight – the ability that some people with striate cortical lesions have to make solid predictions about visual stimuli in the absence of any reported visual awareness – is a paradigmatic example of unconscious perceptual influence on conscious behavior. Newell & Shanks (N&S) are skeptical about the influence of unconscious processes on decision making in blindsight, given that blindsight seems to have alternative explanations that do not appeal to unconscious processes. To back up their claim, they cite research indicating that blindsight may just be degraded visual experience (Campion et al. Reference Campion, Latto and Smith1983; Overgaard Reference Overgaard2011; Weiskrantz Reference Weiskrantz2009). A review of further empirical and theoretical work in the area of blindsight reveals that N&S's conclusions primarily based on Overgaard's (Reference Overgaard2011) findings on blindsight are premature (Brogaard Reference Brogaard2011a; Reference Brogaard2011b; Reference Brogaard2011c; Reference Brogaard2012a; Reference Brogaard2012b; Cowey 2001; Hardin Reference Hardin1985; Heywood & Kentridge Reference Heywood and Kentridge2003; Stoerig & Cowey Reference Stoerig and Cowey1992).
Using a multipoint awareness measurement (PAS), Overgaard (Reference Overgaard2011) shows that the reported degree of conscious experience in blindsight correlates with the blindsight subjects' predictive success in visual tasks. These considerations appear to indicate that it is conscious perception, rather than unconscious processes, that is responsible for blindsighters' predictive behavior. For these reasons, N&S conclude that we need not appeal to unconscious processes in explaining blindsighters' success in decision making. However, Overgaard's studies do not completely rule out that the reported awareness that corresponds to predictive success in blindsight is awareness associated with the higher-order predictive act rather than genuine visual awareness. The subjects may not have the ability to distinguish between being aware of thoughts or judgments and being visually aware of a visual stimuli (Brogaard Reference Brogaard2011a; Reference Brogaard2012b), in which case the PAS studies don't show that unconscious influences are not needed for the predictive behavior.
Further, it's only under forced-choice paradigms that blindsighters are in a position to make predictions about visual stimuli. This suggests that, unlike neurotypical individuals, blindsighters lack full visual awareness in their access to visual information. Even if Overgaard's findings are granted, blindsighters' degraded conscious experience may reflect cognitive access to low-level information deriving from visual, unconscious processes taking place in the retina and the lateral geniculate nucleus (LGN) (and perhaps to some extent in V1). Likewise, the correlation between accurate responses and subjective reports of consciousness may only reflect the subject's level of cognitive access to information derived from visual, unconscious processes. If this is the case, then visual processes that do not correlate with visual awareness may well be at work in blindsighters' decision making, even if the information that is unconsciously processed can be cognitively accessed in forced-choice paradigms. In the light of such observations, N&S's conclusion to the effect that blindsighters' predictive behavior is not influenced by unconscious processes does not hold up.
Theories and research about color processing, together with blindsight data, provide additional evidence that blindsighters must be tapping into unconscious processes in order to make successful predictions about visual stimuli (Brogaard Reference Brogaard2011a; Reference Brogaard2011c). Although blindsight patients have lesions to striate cortex, they can still process information from opponent processes in the retina and the LGN. The Hering–Hurvich–Jameson opponent-process theory is the most popular explanation of how the brain interprets signals from the cones and rods in the retina (Brogaard Reference Brogaard2012a; Hardin Reference Hardin1985). Three types of cones (L for long, M for medium, and S for short) are responsible for detecting chromatic (colored) daylight, while rods are responsible for detecting achromatic (black-white) nightlight. Because the three types of cones overlap in the wavelengths of light they record, color is processed via three opponent channels manifested in bipolar cells. These cells measure differences between red (L) and green (M), blue and yellow (the differences between L plus M and S), and black and white (the sum of L and M). For example, when the activity of M exceeds L, the resulting perceived color is green. When the activity of S exceeds the joint activity of L and M, the perceived color is blue.
Blindsighters can detect these outcomes, and yet they have degraded function of the double opponent cells of striate cortex and in areas upstream from the primary visual cortex. As a result, they cannot detect the standard dimensions of color, such as brightness, saturation and hue. Even if damage to V1 does not prevent weak visual experiences, it does preclude full visual experience of colors (Brogaard Reference Brogaard2011a; Reference Brogaard2011b; Reference Brogaard2011c; Reference Brogaard2012b; Hardin Reference Hardin1985; Stoerig & Cowey Reference Stoerig and Cowey1992). Likewise, people with achromatopsia, which results from a defect to the V4/V8 color complex, lack conscious color experience of the full range of colors (Brogaard Reference Brogaard2011a; Heywood & Kentridge Reference Heywood and Kentridge2003; Heywood et al. Reference Heywood, Kentridge, Cowey, De Gelder, De Haan and Heywood2001).
Despite reporting no or only weak awareness of visual stimuli, blindsighters are able to act reliably in response to wavelengths of light presented to their blind field region, or scotoma. For example, Stoerig and Cowey (Reference Stoerig and Cowey1992) showed that under forced choice, three blindsighters were able to discriminate among narrowband wavelength stimuli despite lacking experience of any conscious visual stimuli. A more recent study showed that inhibiting activity in V1 via transcranial magnetic stimulation (TMS) can result in the absence of color awareness in neurotypical individuals despite the retained ability to discriminate among wavelengths in a forced-choice paradigm (Boyer et al. Reference Boyer, Harrison and Ro2005).
Studies have also shown that blindsighters can be trained to detect wavelengths in the absence of conscious color experience (Bridgeman & Staggs Reference Bridgeman and Staggs1982; Stoerig & Cowey Reference Stoerig and Cowey1992; Zihl Reference Zihl1980; Zihl & Werth Reference Zihl and Werth1984). Stoerig (Reference Stoerig1993) presented the case of patient F.S., who initially, for several years, showed no statistically significant detection of visual stimuli. However, his performance eventually began to improve. The trainability of blindsighters provides further evidence that blindsight patients do in fact lack conscious visual experience. If blindsighters did have degraded visual perception, we should expect subjective reports made by trained subjects to reflect greater visual awareness in correspondence to their improved ability to accurately respond to visual stimuli. This, however, is not the case. Trained blindsighters consistently report no or only weak conscious visual experiences. Although patients such as F.S. consistently report a lack of conscious visual experience, trainability suggests that these blindsighters learn to report on other information that may be easily available for conscious access. In these cases, blindsighters presumably act on the physical bases of color experience despite lacking normal conscious visual experience.
Thus, while visual consciousness may be needed for full visual perception, certain cases show that visual consciousness may not be needed for decision making and judgment.
Cognitive access to information processed unconsciously appears to suffice for reliable decision making in blindsight. In these cases visual information that does not correlate with visual consciousness influences predictions about features of the visual stimuli present in the subject's blind field.
Blindsight – the ability that some people with striate cortical lesions have to make solid predictions about visual stimuli in the absence of any reported visual awareness – is a paradigmatic example of unconscious perceptual influence on conscious behavior. Newell & Shanks (N&S) are skeptical about the influence of unconscious processes on decision making in blindsight, given that blindsight seems to have alternative explanations that do not appeal to unconscious processes. To back up their claim, they cite research indicating that blindsight may just be degraded visual experience (Campion et al. Reference Campion, Latto and Smith1983; Overgaard Reference Overgaard2011; Weiskrantz Reference Weiskrantz2009). A review of further empirical and theoretical work in the area of blindsight reveals that N&S's conclusions primarily based on Overgaard's (Reference Overgaard2011) findings on blindsight are premature (Brogaard Reference Brogaard2011a; Reference Brogaard2011b; Reference Brogaard2011c; Reference Brogaard2012a; Reference Brogaard2012b; Cowey 2001; Hardin Reference Hardin1985; Heywood & Kentridge Reference Heywood and Kentridge2003; Stoerig & Cowey Reference Stoerig and Cowey1992).
Using a multipoint awareness measurement (PAS), Overgaard (Reference Overgaard2011) shows that the reported degree of conscious experience in blindsight correlates with the blindsight subjects' predictive success in visual tasks. These considerations appear to indicate that it is conscious perception, rather than unconscious processes, that is responsible for blindsighters' predictive behavior. For these reasons, N&S conclude that we need not appeal to unconscious processes in explaining blindsighters' success in decision making. However, Overgaard's studies do not completely rule out that the reported awareness that corresponds to predictive success in blindsight is awareness associated with the higher-order predictive act rather than genuine visual awareness. The subjects may not have the ability to distinguish between being aware of thoughts or judgments and being visually aware of a visual stimuli (Brogaard Reference Brogaard2011a; Reference Brogaard2012b), in which case the PAS studies don't show that unconscious influences are not needed for the predictive behavior.
Further, it's only under forced-choice paradigms that blindsighters are in a position to make predictions about visual stimuli. This suggests that, unlike neurotypical individuals, blindsighters lack full visual awareness in their access to visual information. Even if Overgaard's findings are granted, blindsighters' degraded conscious experience may reflect cognitive access to low-level information deriving from visual, unconscious processes taking place in the retina and the lateral geniculate nucleus (LGN) (and perhaps to some extent in V1). Likewise, the correlation between accurate responses and subjective reports of consciousness may only reflect the subject's level of cognitive access to information derived from visual, unconscious processes. If this is the case, then visual processes that do not correlate with visual awareness may well be at work in blindsighters' decision making, even if the information that is unconsciously processed can be cognitively accessed in forced-choice paradigms. In the light of such observations, N&S's conclusion to the effect that blindsighters' predictive behavior is not influenced by unconscious processes does not hold up.
Theories and research about color processing, together with blindsight data, provide additional evidence that blindsighters must be tapping into unconscious processes in order to make successful predictions about visual stimuli (Brogaard Reference Brogaard2011a; Reference Brogaard2011c). Although blindsight patients have lesions to striate cortex, they can still process information from opponent processes in the retina and the LGN. The Hering–Hurvich–Jameson opponent-process theory is the most popular explanation of how the brain interprets signals from the cones and rods in the retina (Brogaard Reference Brogaard2012a; Hardin Reference Hardin1985). Three types of cones (L for long, M for medium, and S for short) are responsible for detecting chromatic (colored) daylight, while rods are responsible for detecting achromatic (black-white) nightlight. Because the three types of cones overlap in the wavelengths of light they record, color is processed via three opponent channels manifested in bipolar cells. These cells measure differences between red (L) and green (M), blue and yellow (the differences between L plus M and S), and black and white (the sum of L and M). For example, when the activity of M exceeds L, the resulting perceived color is green. When the activity of S exceeds the joint activity of L and M, the perceived color is blue.
Blindsighters can detect these outcomes, and yet they have degraded function of the double opponent cells of striate cortex and in areas upstream from the primary visual cortex. As a result, they cannot detect the standard dimensions of color, such as brightness, saturation and hue. Even if damage to V1 does not prevent weak visual experiences, it does preclude full visual experience of colors (Brogaard Reference Brogaard2011a; Reference Brogaard2011b; Reference Brogaard2011c; Reference Brogaard2012b; Hardin Reference Hardin1985; Stoerig & Cowey Reference Stoerig and Cowey1992). Likewise, people with achromatopsia, which results from a defect to the V4/V8 color complex, lack conscious color experience of the full range of colors (Brogaard Reference Brogaard2011a; Heywood & Kentridge Reference Heywood and Kentridge2003; Heywood et al. Reference Heywood, Kentridge, Cowey, De Gelder, De Haan and Heywood2001).
Despite reporting no or only weak awareness of visual stimuli, blindsighters are able to act reliably in response to wavelengths of light presented to their blind field region, or scotoma. For example, Stoerig and Cowey (Reference Stoerig and Cowey1992) showed that under forced choice, three blindsighters were able to discriminate among narrowband wavelength stimuli despite lacking experience of any conscious visual stimuli. A more recent study showed that inhibiting activity in V1 via transcranial magnetic stimulation (TMS) can result in the absence of color awareness in neurotypical individuals despite the retained ability to discriminate among wavelengths in a forced-choice paradigm (Boyer et al. Reference Boyer, Harrison and Ro2005).
Studies have also shown that blindsighters can be trained to detect wavelengths in the absence of conscious color experience (Bridgeman & Staggs Reference Bridgeman and Staggs1982; Stoerig & Cowey Reference Stoerig and Cowey1992; Zihl Reference Zihl1980; Zihl & Werth Reference Zihl and Werth1984). Stoerig (Reference Stoerig1993) presented the case of patient F.S., who initially, for several years, showed no statistically significant detection of visual stimuli. However, his performance eventually began to improve. The trainability of blindsighters provides further evidence that blindsight patients do in fact lack conscious visual experience. If blindsighters did have degraded visual perception, we should expect subjective reports made by trained subjects to reflect greater visual awareness in correspondence to their improved ability to accurately respond to visual stimuli. This, however, is not the case. Trained blindsighters consistently report no or only weak conscious visual experiences. Although patients such as F.S. consistently report a lack of conscious visual experience, trainability suggests that these blindsighters learn to report on other information that may be easily available for conscious access. In these cases, blindsighters presumably act on the physical bases of color experience despite lacking normal conscious visual experience.
Thus, while visual consciousness may be needed for full visual perception, certain cases show that visual consciousness may not be needed for decision making and judgment.
Cognitive access to information processed unconsciously appears to suffice for reliable decision making in blindsight. In these cases visual information that does not correlate with visual consciousness influences predictions about features of the visual stimuli present in the subject's blind field.