Nivedita Gangopadhyay, Michael Madary, and Finn Spencer (Eds.), Perception, Action, and Consciousness: Sensorimotor Dynamics and the Two Visual Systems

Oxford University Press, 2010, 303 pp.,

ISBN: 9780199551118, $ 85.00

Ellen Fridland

Berlin School of Mind and Brain

Humboldt University of Berlin

Perception, Action, and Consciousness is a volume devoted to exploring the tensions and potential routes for reconciliation between two types of approaches to visual perception: the sensorimotor, action-oriented view of perception and the two visual systems hypothesis. These views hold conflicting positions as to the contribution that action makes to the qualitative character of a perceptual event. The action-oriented or sensorimotor views represented here, to varying degrees, hold that action plays a central, even constitutive role, in determining the phenomenal character of visual experience. In contrast, the two visual systems model is committed to the idea that action and visual perception are processed independently and, thus, remain functionally distinct. Accordingly, the two visual systems model holds that the dorsal stream, which is responsible for processing vision for action, has no direct impact on conscious perceptual experience, which is processed separately by the ventral stream.

This volume is essential reading for any philosopher of perception or vision researcher interested in the relationship between action and perception. The volume contains several contributions, which both frame and advance the debate between the two systems theorists and the adherents of the sensorimotor view. This book is exceptional in several ways that relate to interaction and communication: (1) this is a truly interdisciplinary volume with contributions from philosophers, psychologists, neurologists, and cognitive neuroscientists, and (2) theorists and scientists are actually talking to one another: responding to objections, considering each-other’s claims, developing each other’s points, proposing solutions, and trying to decipher a way forward. This volume embodies the spirit and rigor of the theorist to whom it is dedicated, Susan Hurley.

The volume is organized into six sections, each of which contains contributions by major players in the action and perception debate. Each essay is complete with an abstract. As such, instead of summarizing individual articles, I will focus on the feature that I take to be most remarkable about this collection: namely, how various researchers respond to and build upon each other’s work. I will focus on three particular instances of interaction in the volume and end by gesturing towards a potentially fruitful, but overlooked avenue for reconciliation.

In the first section, I will present David Milner and Melvyn Goodale’s response to objections raised both by Yves Rosetti et al. and Dean R. Melmouth et al. concerning the functional double-dissociation of the ventral and dorsal streams. In the second section, I will focus on Alva Noë’s response to Mohan Mathen’s intriguing proposal concerning the qualitative contribution that dorsal stream processing makes to visual experience. In the third section, I will present Pierre Jacob and Frédérique de Vignemont’s attempts to wade through some hairy issues that Andy Clark raises about the complexity of consciousness. And lastly, I will point out that while several authors have been tempted to dissipate the tension between action-oriented approaches and the two visual streams model by emphasizing interaction, none have explored the seemingly promising route of investigating the relationship between the ventral and dorsal stream in the development of embodied skill.

Part I: Double dissociations—objections and responses

One recurring theme in this anthology is the question of whether, in fact, a double-dissociation between ventral and dorsal stream processing obtains. Goodale and Milner insist that brain lesions and perceptual illusions support a strict processing division while theorists like Rossetti et al. and Melmouth et al. forward challenges to their position.

Very simply, Milner and Goodale’s famous two visual systems theory rests on the claim that the ventral stream of visual processing is responsible for conscious qualitative perceptual experience, while the dorsal stream is responsible for the fine-grained motor coordination required for action instantiation. As such, they claim that the ventral stream is responsible for “vision for perception” and the dorsal, “vision for action.” Milner and Goodale claim that the two streams interact only insofar as the ventral stream selects the goals for action and the dorsal stream carries out the movements required for satisfying these goals. Beyond this interaction of setting and fulfilling goals, the streams are functionally independent. Milner and Goodale ground their claims for the independence of vision for action and vision for perception on two sets of evidence: (1) cases of brain lesions which result in characteristic deficits of either conscious perception (as in visual agnosia, which results from ventral stream lesions) or in errors of reaching in grasping (as in optic ataxia, which results from lesions in the dorsal stream) and (2) studies which show that, even in healthy subjects, perceptual illusions can differentially effect conscious perception and reaching and grasping movements.

Rossetti et al.’s objection to the two visual systems theory focuses on questioning the purported symmetry between visual agnosia and optic ataxia. In turn, Melmouth et al. challenge Milner and Goodale by providing evidence of the Poggendorff Illusion—a perceptual illusion that equally effects both conscious visual perception and fine-grained motor activity.

Rossetti et al. claim that evidence from patients with lesions resulting in visual agnosia and optic ataxia does not support a functional dichotomy between vision for perception and vision for action, but rather, a distinction between central visual processing and peripheral visual processing. Rossetti et al. draw this conclusion on the basis of studies that show that optic ataxics express deficits in reaching and grasping in peripheral vision but do not display similar deficits in central vision. They bolster their claim by arguing that if the two visual systems hypothesis were correct, then optic ataxics should be severely handicapped in their daily lives. In fact, however, patients with optic ataxia do not complain of pronounced difficulties performing everyday activities. Rossetti et al. further claim that the delays introduced between a target presentation and pointing have nonsymmetrical effects on patients with optic ataxia and visual agnosia. That is, introducing a delay between target presentation and pointing resulted in huge reaching errors for DF, a patient with visual agnosia, but there were no corresponding increases in performance for patients with optic ataxia in central vision. These patients showed improvement with the introduction of a delay only in peripheral vision. Again, Rossetti et al. insist that the dissociation of ventral and dorsal stream processing is not best construed as a dissociation between vision for conscious perception and vision for fine-grained motor action, but rather, as a dissociation between vision in the peripheral and vision in the central field.

Milner and Goodale respond to Rossetti et al. by pointing out that the evidence for a symmetrical dissociation, especially in patients with optic ataxia who show reaching errors in central vision is, in fact, more robust than Rossetti et al. suggest. Milner and Goodale also argue that the reason that patients with optic ataxia show less marked reaching and grasping errors in central vision is not because the ventral stream normally directs visuomotor tasks in the central field, but because patients with optic ataxia compensate for abnormal dorsal-stream-directed action by relying on ventral stream processing. Accordingly, since the ventral stream produces a stronger representation in central vision than peripheral vision, patients with optic ataxia, compensating for dorsal stream inadequacy by relying on ventral stream processing, show less drastic deficits in central vision. In effect, Milner and Goodale claim that patients with optic ataxia “revert to the unskilled strategy that we all use when beginning to master a novel visuomotor act” in order to compensate for dorsal stream deficiency. They claim that it is as a result of this kind of compensation that patients with lesions in their dorsal stream overcome prominent everyday handicaps, and also, why delays between target presentation and pointing result in an increase in performance for patients with optic ataxia, especially in the peripheral field.

In a second challenge to Milner and Goodale, Melmouth et al. present experimental evidence of the Poggendorff Illusion, a perceptual illusion that impacts both visual perception and perception for action. Melmouth et al. claim that it is unclear from the evidence whether the illusion effects both vision and action because the relevant features are processed in early vision (EV), before the split of the ventral and dorsal streams, or if the illusion results from a lack of online visual feedback directing accurate perceptual representation of the target, as suggested by Franz et al. (2008). The significance of the Melmouth et al. study is to show that their results are compatible with both the Milner and Goodale and the Franz et al. interpretation.

Predictably, Milner and Goodale claim that the Poggendorff Illusion impacts both conscious perception and perception for action because the features relevant to the illusion are processed in EV, prior to the split of the dorsal and ventral streams. As such, the features processed in EV are carried through to both visual perception and vision for action. Further, Milner and Goodale reprimand Franz et al. (though it is unclear to what extent Melmouth et al. are implicated here, too) for using awkward movements and intrusive recording devices in order to study the effects of perceptual illusions on the dorsal stream. Milner and Goodale claim that such actions do not implicate dorsal stream processing, but rather, vision for perception, which is responsible for guiding novel, unpracticed actions. As such, Milner and Goodale conclude that illusions that appear to effect action, but rely on awkward movements, do not provide evidence of the susceptibility of the dorsal stream to perceptual illusions.

Part II:

In a particularly fascinating paper, Mohan Mathen proposes that dorsal stream processing, or what he calls “motion-guiding vision,” is responsible for contributing a “feeling of presence” to visual experience. Mathen argues that visual contents can be the objects of various kinds of attitudes, some truth or actuality-committing like beliefs, but others, like hopes or wishes, not actuality-committing. For example, the visual experience of a picture of an elephant is not actuality-committing. It does not seem to us that there is actually an elephant present when we look at the picture. It does not engender in us a feeling of presence—it does not afford action. In contrast, the visual experience of a real elephant is actuality-committing. Seeing a real elephant commits us to the existence of the elephant in front of us. It fosters in us a feeling of presence—it feels like there are different ways for us to act on the elephant. E.g., we can walk around it, climb it, feed it, ride it, etc.

Mathen argues that the difference between looking at a photograph of an elephant, and at an elephant itself, is not to be found in the content of the visual representation, but in the attitude that we take toward that representation. One attitude fosters a “feeling of presence” while another does not. Mathen claims that it is motion-guiding vision that is responsible for generating a perceptual attitude, which spawns the qualitative feeling of presence. It is motion-guiding vision that makes us feel as though we can act on certain scenes. As such, whereas Milner and Goodale claim that the outputs of dorsal stream processing remain thoroughly unconscious, Mathen holds that motion-guiding vision creates “an indexical or demonstrative form of conscious content.” He attributes the generation of the feeling of presence that accompanies ordinary visual experiences of a perceptual array, that is, an array on which we feel it is possible to act, to the processing of vision for action.

In his paper, Alva Noë is concerned, first and foremost, with arguing that the enactive theory of perception and the two visual systems hypothesis are not, in principle, mutually exclusive. Rather, he claims that the two visual systems model needs enactive perception in order to account for the interaction between the ventral and dorsal streams. In his paper, Noë also takes the time to respond to Mathen’s proposal concerning the connection between motion-guiding vision and the feeling of presence. Noë appeals to neurological evidence from persons with optic ataxia, a condition that results from lesions in the dorsal stream, who nonetheless have very little discernable trouble in everyday life. Noë claims that if motion-guiding vision were responsible for the feeling of presence in ordinary perceptual experiences, then patients with optic ataxia could not fail to both notice and be severely afflicted by their dorsal stream deficits. Noë concludes that since this situation does not obtain, it is impossible that motion-guiding vision is responsible for the feeling of presence in normal, conscious, visual experience.

Part III: Sifting through consciousness

Andy Clark challenges the two visual systems hypothesis (and really, everyone involved in the action and perception debate) by highlighting various shaky background assumptions concerning the nature of consciousness that are implicated in the disagreement. Clark argues that conscious experience may be

“a rough and ready label for a typically integrated, but potentially highly dissociable, complex of capacities. Some of these involve recall and report, some involve attention and noticing, others…involve only various forms of recurrent processing amplified by neural activity. Such a model would be an instance of what Sloman (2007) calls a ‘labyrinthine’ theory according to which visual experience is itself highly structured, and multiple layered, such that different combination of many bits of the labyrinth determine different (often dissociable) aspects and nuances of what we have come to think of as ‘our visual experience.’”

Importantly, in order to establish the functional independence of vision for perception and vision for action, as Milner and Goodale attempt to, Clark claims that they must assume that conscious experience is simple, unified, and well-defined. In short, given that Milner and Goodale easily decipher the functional dichotomy between ventral and dorsal stream contributions to conscious perceptual experience, they, at least tacitly, must be working with a simple or narrow conception of conscious experience.

In addition to raising this foundational concern regarding the nature of consciousness, Clark focuses on a particular ‘radical challenge’ for distinguishing between conscious and nonconscious states. This challenge arises when we drive a wedge between various kinds of access and reportability on the one hand and consciousness on the other. The worry is especially poignant if we accept that conscious perceptual experience may ‘overflow’ cognitive access, and thus, become undetectable by the standard measures used by Milner and Goodale. Clark insists that to be conscious an experience must be poised for potential integration into at least some personal level processes, but accepts that such states may remain unreportable. In light of these considerations, the issue about which kinds of states are involved in visual agnosia (conscious and not reportable or conscious and not actually accessed, or nonconscious, full stop) remains an open question.

Taking up the challenge of answering this question, Jacob and de Vignemont produce several sophisticated considerations, which ultimately lead to further questions about the possibility of visual awareness in the absence of normal ventral stream processing. Because Jacob and de Vignemont accept that consciousness outstrips reportability, they go on to produce three further considerations relevant for deciding whether DF, the famous visual agnosia patient, experiences phenomenal consciousness of visual properties. The most interesting of these considerations focuses on the role of unbound features in conscious perception. Relying on Schenk and Milner’s (2006) studies proving that DF uses width information in order to produce accurate guesses regarding shape, Jacob and de Vignemont ask whether it might be possible that DF is visually conscious of width. In reflecting on this issue, Jacob and de Vignemont emphasize that the property of width is not identical to the property of shape. Width, it turns out, is an unbound property. As such, in order to establish that DF has phenomenal experience of width, one would have to show that it is in general possible to have a qualitative experience of unbound properties. Though this remains an open empirical question, we should note that there is, thus far, no positive evidence suggesting that such a possibility exists.

Part IV: Skill learning and interaction

Several theorists in this volume attempt to bridge the divide between the action-oriented and two visual systems views by focusing on interaction. For example, as I indicated above, Noë argues that the two visual systems theorists must make use of action-oriented theories in order to account for the interaction between the ventral and dorsal streams. Julian Kiverstein, also worried about interaction, focuses on resolving the problem of communication. This problem arises because, as the two visual systems theory holds, information in the two streams is coded in different, seemingly incompatible, frames of reference. Further, Rossetti et al. and Vallar and Mancini come at interaction from an anatomical perspective, suggesting that there is an important functional role played by the brain regions lying in between the dorsal and ventral streams.

Though interaction between the ventral and dorsal streams is a recurring theme in this volume, I was surprised that no contribution investigated the diachronic interaction between conscious perception and action, which takes place during embodied skill learning. As Milner and Goodale admit,

“Not all movements will be mediated by the ‘encapsulated’ visuomotor networks in the dorsal stream. The more unpracticed and novel the action, the more likely it is to require a good deal of cognitive supervision and thereby to be influenced by perceptual processing. The first time you use chopsticks, for example, you are vividly aware of what you are doing and you monitor your movements quite consciously, something you do not do when using your fingers, or even a fork, to pick up food. Presumably, this conscious monitoring of unpractised movements depends on information provided by the perceptual networks in the ventral stream… Once the action is well-practised and becomes automatized, however, it seems that control of the constituent movement is passed to the visuomotor networks in the dorsal stream.”

In the case of overlearned skills, it would seem that the automatic processing of the dorsal stream, though synchronically independent from ventral stream processing, is diachronically dependent on and determined by conscious visual perception. Because the ventral stream guides and directs actions prior to their automatization, we have a clear case of informational processing, the details of which are determined by vision for perception, being integrated or incorporated into the processing of the vision for action stream. Of course, this does not give us a path from the dorsal stream back to the ventral stream, that is, it does not give us a way to understand the qualitative character of a perceptual event as being dependent on action, but it does give us a substantive connection between the function computed by the dorsal stream and that of ventral stream processing.

Conclusion:

There are several notable and substantive contributions that I was not able to note in this review. Many essays, besides the ones that I have mentioned, put forth novel approaches to and relevant evidence for the action and perception debate. In all, this volume is, to my knowledge, the best collection of work exploring the tensions and issues that arise when considering action-oriented theories of perception together with the two visual systems approach. It is a well-organized, careful, and overall imaginative collection of essays.

REFERENCES:

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Blangero, A., Gaveau, V., Luauté, R., Rode, G., Salemme, R., Boisson, D. et al. (2008). A hand and a field effect on on-line motor control in unilateral optic ataxia. Cortex, 46, 77-93.

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Djikerman, H., McIntosh, R., Anema, H., de Haan, E., Kapelle, L., & Milner, A. (2005). Reaching errors in optic ataxia are linked to eye position rather than head or body position. Neuropsychologia, 44, 2766-2773.

Dretske, F. (2006). Perception without awareness. In T. Gendler and J. Hawthorne (Eds.), Perceptual Experience (pp.147-180). New York: Oxford University Press.

Fodor, J. (2007). The revenge of the given. In B.P. McLaughlin and J. Cohen (Eds.), Contemporary debates in philosophy of mind (pp. 105-116) . Oxford: Blackwell.

Franz, V.H., Hesse, C., and Collath, S. (2008). Visual Illusion, delayed grasping and memory: no shift from dorsal to ventral control. Neuropsychologia 25: 920-950.

Gaveau, V., Pélisson, D., Blangero, Al, Urquizar, C., Prablanc, C., Vighetto, A. et al. (2008). A common parietal module for saccade and reach: eye-hand coordination and saccadic control in optic ataxia. Neuropsychologia, 46, 475-486.

Himmelbach, M. & Karnath, H.O. (2005). Dorsal and ventral stream interaction: contributions from optic ataxia. Journal of Cognitive Neuroscience, 17, 632-640.

Hurl

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Hurley, S., & Noë, A. (2003). Neural plasticity and consciousness. Biology and Philosophy, 18, 131-168.

Kahn, A., Pisella, L., Vighetto, A., Cotton, F., Luauté, J., Boisson, D. et al. (2005). Optic ataxia errors depend on remapped, not viewed, target location. Nature Neuroscience, 8, 418-420.

Landman, R., Sperkreijse, H., Lamme, V. (2003). Large capacity storage of integrated objects before change blindness. Vision Research, 43, 149-164.

Milner, D. & Goodale, M. (1995). The visual brain in action. Oxford: Oxford University Press.

Milner, A., Paulignan, Y., Djikerman, H., Michel, F., & Jeannerod, M. (1999). A paradoxical improvement of misreaching in optic ataxia: new evidence fort two separate neural systems for visual localization. Proceedings: Biological Sciences, 266, 2225-2229.

Milner, A., & Goodlae, M. (2008). Two visual systems re-viewed. Neuropsychologia, 46, 774-785.

Noë, A. (2004). Action in Perception. Cambridge, MA: MIT Press.

O’Regan, J.K., and Noë, A. (2001). A sensorimotor approach to vision and visual consciousness. Behavioral and Brain Sciences, 24, 883-975.

Pisella, L., Sergio, L., Blangero, A., Torchin, L., Vighetto, A., & Rossetti, Y. (2009). Contributions of the dorsal stream to perception and action. Neuropsychologia, 47, 3033-3044.

Revol , P., Rosetti, Y., Vighetto, A., & Pisella., L. (2003). Pointing errors in immediate and delayed conditions in unilateral optic ataxia. Spatial Vision, 16, 347-364.

Rice, N., Edwards, M., Schindler, I., Punt, T., McIntosh, R., Humphreys, G. et al. (2008). Delay abolishes the obstacle avoidance deficit in unilateral optic ataxia. Neuropsychologia, 46, 1549-1557.

Rossetti, Y., Vighetto, A., & Pisello, L. (2003). Optic ataxia revisited: immediate motor control versus visually guided action. Experimental Brain Research, 153, 171-179.

Rossetti, Y., Revol, P., McIntosh, R., Pisella, L., Rode, G., Danckert, J. et al. (2005). Visually guided reaching: bilateral posterior parietal lesions cause a switch from fast visuo-motor to slow cognitive control. Neuropsychologia, 43, 162-177.

Schenk, T. and Milner, D.M. (2006). Concurrent visuo-motor behavior improves form discrimination in patient with visual from agnosia. European Journal of Neuroscience 24: 1495-1503.

Sperling, G. (1960). The information available in brief visual presentations. Psychological Monographs, 74, 1-29.

First developed by Hurley (1998); O’Regan and Noë (2001); Hurley and Noë (2003); Noë (2004).

Famously defended by Milner and Goodale (1995).

See, especially, O’Regan’s and Noë’s contributions for a representation of the enactive view, which holds that knowledge of sensorimotor contingencies is constitutive of the qualitative character of visual perception. For some variations on this action-oriented approach, see Schellenberg, Kiverstein, and Mathen. All in Perception, Action, and Consciousness (hereon, PAC).

See also, Milner and Goodale (1995).

See, for instance, Blangero et al. (2007,2008); Djikermann et al. (2005); Gaveau et al. (2008); Khan et al. (2005); Revol et al. (2003); and Rice et al. (2008); Himmelbach et al. (2005); Rossetti et al. (2005).

Rossetti et al. (2003); Pisella et al. (2009).

Milner et al. (2008).

Milner et al. (1999); Rossetti et al. (2005).

PAC, p.90

PAC, p.107

Rossetti et al. (2003); Pisella et al. (2009).

PAC, p. 65

For evidence supporting this view see Sperling (1960); Landman et al. (2003). In defense of this interpretation, see Block (2007); Dretske (2006); and Fodor (2007).

PAC, pg. 83

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Ellen Fridland

2012-05-06

CUNY