Cognitive neuroscientist with a background in ecological psychology. Attempting to work out the implications of embodied and situated cognition for our understanding of the nervous system and its role in perception and action. Recipient of the Li Ka Shing Prize. See my lab website (Wordpress link below) for more information.
The Modern Legacy of Gibson's Affordances for the Sciences of Organisms, 2024
In the ecological approach to perception and action, information that specifies affordances is av... more In the ecological approach to perception and action, information that specifies affordances is available in the energy arrays surrounding organisms, and this information is detected by organisms in order to perceptually guide their actions. At the behavioral scale, organisms responding to affordances are understood as self-organizing and reorganizing softly-assembled synergies. Within the ecological community, little effort has so far been devoted to studying this process at the neural scale, though interest in the topic is growing under the header of ecological neuroscience. From this perspective, switches between affordances may be conceptualized as transitions within brain-body-environment systems as a whole rather than under the control of a privileged (neural) scale. We discuss extant empirical research at the behavioral scale in support of this view as well as ongoing and planned work at the neural scale that attempts to further flesh out this view by characterizing the neural dynamics that are associated with these transitions while participants dynamically respond to affordances.
Frontiers in Psychology: Theoretical and Philosophical Psychology, 2022
Mainstream cognitive neuroscience aims to build mechanistic explanations of behavior by mapping a... more Mainstream cognitive neuroscience aims to build mechanistic explanations of behavior by mapping abilities described at the organismal level via the subpersonal level of computation onto specific brain networks. We provide an integrative review of these commitments and their mismatch with empirical research findings. Context-dependent neural tuning, neural reuse, degeneracy, plasticity, functional recovery, and the neural correlates of enculturated skills each show that there is a lack of stable mappings between organismal, computational, and neural levels of analysis. We furthermore highlight recent research suggesting that task context at the organismal level determines the dynamic parcellation of functional components at the neural level. Such instability prevents the establishment of specific computational descriptions of neural function, which remains a central goal of many brain mappers – including those who are sympathetic to the notion of many-to-many mappings between organismal and neural levels. This between-level instability presents a deep epistemological challenge and requires a reorientation of methodological and theoretical commitments within cognitive neuroscience. We demonstrate the need for change to brain mapping efforts in the face of instability if cognitive neuroscience is to maintain its central goal of constructing computational mechanistic explanations of behavior; we show that such explanations must be contextual at all levels.
Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways ... more Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15 (1), 20–25] proposal to distinguish the dorsal and ventral systems on basis of the functional demands they serve (i.e., action and perception), a vast literature has emerged that scrutinized if the dorsal and ventral systems indeed process information into egocentric and allocentric codes in accordance with their respective functions. However, a corollary of Goodale and Milner’s original proposal, that these functional demands also impose different constraints on information detection, has been largely overlooked. In the present study, we measured gaze patterns to investigate how information detection for action and perception differs. In two conditions, participants (N=9) grasped or made a manual estimate of the length of a shaft embedded in a Müller-Lyer configuration. The illusion significantly affected the manual estimates, but not...
Limb apraxia is evident in approximately 50% of patients after left hemisphere cerebral vascular ... more Limb apraxia is evident in approximately 50% of patients after left hemisphere cerebral vascular accident (LCVA) and increases disability and caregiver dependence. Individuals with apraxia exhibit abnormalities in spatio-temporal aspects of gesture production and/or in knowledge of tool-related actions (action semantics). This preliminary study of three LCVA participants aimed to (i) explore the efficacy of a novel Action Network Treatment (ANT) that focused on improving the semantic association between tool actions and other types of tool knowledge, an intervention inspired by successful semantic network treatments in aphasia (e.g., Edmonds et al., 2009), and (ii) explore whether there are individuals with apraxia who benefit from ANT relative to a version of a comparatively well-studied existing apraxia treatment (Smania et al., 2006; Smania et al., 2000) that shapes gesture via focus on practicing the spatio-temporal aspects of gesture production (Tool Use Treatment or TUT). One participant demonstrated treatment benefits from both ANT and TUT, while another only benefited from TUT. These findings indicate that our novel semantic network strengthening approach to gesture training may be efficacious in at least some individuals with apraxia, and provide a foundation for future study of the characteristics of people with apraxia who benefit from each approach.
Modulation of excitability in the motor system can be observed before overt movements but also in... more Modulation of excitability in the motor system can be observed before overt movements but also in response to covert invitations to act. We asked whether such changes can be induced in the absence of even covert motor instructions, namely, as a function of the location of the hand with reference to the body. Participants received single-pulse TMS over the motor cortex while they placed their contralateral hand (right hand in Experiment 1, left hand in Experiment 2) to the right or left of their body midline, and looked either at or away from their hand. In both experiments, greater excitability was observed when gaze was directed to the right. This finding is interpreted as a consequence of left brain later- alization of motor attention. Contrary to our expectations, we furthermore consistently observed greater excitability when gaze was directed away from the hand. To account for this finding, we introduce the concept of “surveillance attention” which, we speculate, modulates cortical gain, and thereby cortical excitability. Its function is to increase read- iness to act in non-foveated regions of space. Such a process confers an advantage in environments, like those in which humans evolved, in which threatening stimuli may appear unexpectedly, and at any time.
Ecological psychology has been criticized for ignoring the brain in its theory formation. In rece... more Ecological psychology has been criticized for ignoring the brain in its theory formation. In recent years, however, a number of researchers have started asking ecologically-inspired questions about the ways in which not only the embodied activity of the organism in its environment, but also the particulars of the organism's nervous system matter. This work has typically appeared in neuroscience journals, thereby potentially escaping the attention of ecological psychologists. The current article introduces a Special Issue of Ecological Psychology that aims to correct this problem. This Issue brings together one empirical and six theoretical articles that develop ideas about the contributions of the nervous system to perception-action. We briefly review each of the articles, identify common themes, and point out the surprising variety in theoretical positions. It is hoped that this Special Issue will help guide discussions amongst ecological psychologists and (ecological) neuroscientists as they confront the question “What should a ‘Gibsonian neuroscience’ look like?”
Rahnev and Denison addressed the issue of (sub)optimalities in perception but only made a passing... more Rahnev and Denison addressed the issue of (sub)optimalities in perception but only made a passing reference to evolutionary thinking. In our commentary, we concur with the authors' claim that evolution does not work towards optimalities, but argue that an evolutionary perspective on perception questions the Bayesian approach that the authors adopted.
Objectives: Adaptive interaction with the environment requires the ability to predict both human ... more Objectives: Adaptive interaction with the environment requires the ability to predict both human and non-biological motion trajectories. Prior accounts of the neurocognitive basis for prediction of these two motion classes may generally be divided into those that posit that non-biological motion trajectories are predicted using the same motor planning and/or simulation mechanisms used for human actions, and those that posit distinct mechanisms for each. Using brain lesion patients and healthy controls, this study examined critical neural substrates and behavioral correlates of human and non-biological motion prediction. Methods: Twenty-seven left hemisphere stroke patients and 13 neurologically intact controls performed a visual occlusion task requiring prediction of pantomimed tool use, real tool use, and non-biological motion videos. Patients were also assessed with measures of motor strength and speed, praxis, and action recognition. Results: Prediction impairment for both human and non-biological motion was associated with limb apraxia and, weakly, with the severity of motor production deficits, but not with action recognition ability. Furthermore, impairment for human and non-biological motion prediction was equivalently associated with lesions in the left inferior parietal cortex, left dorsal frontal cortex, and the left insula. Conclusions: These data suggest that motor planning mechanisms associated with specific loci in the sensorimotor network are critical for prediction of spatiotemporal trajectory information characteristic of both human and non-biological motions. (JINS, 2017, 23, 171–184)
Gibson argued that illusory pictorial displays contain "inadequate" information (1966, p. 288) bu... more Gibson argued that illusory pictorial displays contain "inadequate" information (1966, p. 288) but also that a "very special kind of selective attention" (p. 313) can dispel the illusion—suggesting that adequate perceptual information could in fact be potentially available to observers. The present paper describes Gibson's treatment of geometrical illusions and reviews pertinent empirical evidence. Interestingly, Gibson's insights have been corroborated by recent findings of inter- and intra-observer variability in susceptibility to visual illusions as a function of culture, learning and task. It is argued that these findings require a modification of the general Gibsonian principle of perception as the detection of specifying information. Withagen and Chemero's (2009) evolutionary motivated reconceptualization of perception predicts observers' use of both specifying and non-specifying information and inter- and intra-observer variability therein. Based on this reconceptualization we develop an ecological approach to visual illusions that explains differential illusion effects in terms of the optical variable(s) detected.
The dominant view of the ventral and dorsal visual systems is that they subserve perception and a... more The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters (2011) suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching (perception), pointing (action) and perceptual judgment responses to masked Müller–Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length at brief durations remained sensitive to veridical stimulus length (egocentric information), but not the illusion (allocentric, context-dependent information), which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception (matching) or action (pointing) responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric and slower allocentric information pick up, respectively.
There is ongoing debate with respect to interpretation of the finding that, in contrast to percep... more There is ongoing debate with respect to interpretation of the finding that, in contrast to perceptual size judgments, actions are relatively unaffected by the Müller–Lyer illusion. In normal unrestricted viewing situations observers cannot perform an action directed at an object without simultaneously perceiving the object – this makes it difficult to unequivocally establish whether observed effects are a function of vision for perception, vision for action, a combination of both, or of a single all-purpose visual system. However, there is evidence that observers are capable of performing actions towards objects of which they are not consciously aware, implying that two distinct visual thresholds may exist; one accompanying vision for action and one accompanying vision for perception. To investigate this possibility we created a situation in which visual information was presented below the perception threshold, but above the purported action threshold, allowing examination of action responses independent of contributions from vision for perception. Following a perceptual categorization task, participants performed delayed pointing movements towards briefly exposed masked Müller–Lyer targets of different sizes. When the targets were presented below the perception threshold, participants were unable to discriminate between them, yet their delayed pointing movements were affected by target size (but not the illusion). The results imply that vision for action is functional even after a delay and/or that the pickup of egocentric information is associated with a lower visual threshold than the pickup of allocentric information.
Based upon evidence that vision for action has quicker access to visual information than vision f... more Based upon evidence that vision for action has quicker access to visual information than vision for perception, we hypothesized that the two systems may have differentiated visual thresholds. There is also evidence that, unlike vision for perception, vision for action is insensitive to cognitive dual-task interference. Using visual masking, we determined the visual thresholds of 15 participants in a perception task, an action task and an action plus concurrent cognitive secondary task. There was no difference in threshold between the perception task and the action task, but the action plus concurrent secondary task was accompanied by a greater visual threshold than both the perception task and the action task alone, indicating dual-task interference. The action task was thus most likely informed by vision for perception. The implications of these results are reviewed in the context of recent discussions of the two visual systems model.
Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways ... more Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15 (1), 20–25] proposal to distinguish the dorsal and ventral systems on basis of the functional demands they serve (i.e., action and perception), a vast literature has emerged that scrutinized if the dorsal and ventral systems indeed process information into egocentric and allocentric codes in accordance with their respective functions. However, a corollary of Goodale and Milner’s original proposal, that these functional demands also impose different constraints on information detection, has been largely overlooked. In the present study, we measured gaze patterns to investigate how information detection for action and perception differs. In two conditions, participants (N=9) grasped or made a manual estimate of the length of a shaft embedded in a Müller-Lyer configuration. The illusion significantly affected the manual estimates, but not the hand aperture during grasping. In line with these behavioral findings, significant differences in gaze patterns were revealed between the two tasks. Participants spent more time looking at areas that contain egocentric information (i.e., centre of the shaft) when grasping as compared to making a manual length estimate. In addition, participants, made more gaze shifts (i.e., especially between the two areas surrounding the shaft endpoints and including the arrowheads) when making the manual length estimate, enabling the pick up of allocentric information. This difference was more pronounced during task execution as compared to task preparation (i.e., before movement onset). These results support the contention that the functional distinction between the dorsal and ventral systems is not limited to the processing of information, but also encompasses the detection of information.
In the present study, we examined whether individual differences in the perception of illusory Ju... more In the present study, we examined whether individual differences in the perception of illusory Judd drawings point to variability in the pickup of informational variables. Two sources for these individual differences were addressed: culture and learning. East Asian (n = 24) and Western (n = 24) participants made perceptual judgments of the midpoint of the shaft of various Judd figures in a pretest–practice–posttest design. During practice, half of the participants received feedback about the actual midpoint after each trial, while the other half did not receive feedback. The results showed differences among perceivers of different cultures in judging the midpoints of the shafts of Judd figures, particularly with respect to their propensity to improve perceptual accuracy after repeated practice and feedback. For most participants, changes in illusory bias as a consequence of learning were shown to reflect either a change in what informational variable they exploited or a rescaling or calibration of the perception to the informational variable. However, the individual differences in illusory bias related to culture could not be unequivocally attributed to either of these perceptual-learning processes.
Avant: Journal of the Philosophical-Interdisciplinary Vanguard , 2012
Gibson developed the affordance concept to complement his theory of direct perception that stands... more Gibson developed the affordance concept to complement his theory of direct perception that stands in sharp contrast with the prevalent inferential theories of perception. A comparison of the two approaches shows that the distinction between them also has an ontological aspect. We trace the history and newer formalizations of the notion of affordance and discuss some competing opinions on its scope. Next, empirical work on the affordance concept is reviewed in brief and the relevance of dynamical systems theory to affordance research is demonstrated. Finally, the striking but often neglected convergence of the ideas of Gibson and those of certain Continental philosophers is discussed.
We investigated whether the control of movement of the left hand is more likely to involve the us... more We investigated whether the control of movement of the left hand is more likely to involve the use of allocentric information than movements performed with the right hand. Previous studies (Gonzalez et al. in J Neurophys 95: 3496–3501, 2006; De Grave et al. in Exp Br Res 193: 421–427, 2009) have reported contradictory findings in this respect. In the present study, right-handed participants (N=12) and left-handed participants (N=12) made right-and left-handed grasps to foveated objects and peripheral, non-foveated objects that were located in the right or left visual hemifield and embedded within a Müller-Lyer illusion. They were also asked to judge the size of the object by matching their hand aperture to its length. Hand apertures did not show significant differences in illusory bias as a function of hand used, handedness or visual hemifield. However, the illusory effect was significantly larger for perception than for action, and for the non-foveated compared to foveated objects. No significant illusory biases were found for reach movement times. These findings are consistent with the two-visual system model that holds that the use of allocentric information is more prominent in perception than in movement control. We propose that the increased involvement of allocentric information in movements toward peripheral, non-foveated objects may be a consequence of more awkward, less automatized grasps of nonfoveated than foveated objects. The current study does not support the conjecture that the control of left-handed and right-handed grasps is predicated on different sources of information.
The Modern Legacy of Gibson's Affordances for the Sciences of Organisms, 2024
In the ecological approach to perception and action, information that specifies affordances is av... more In the ecological approach to perception and action, information that specifies affordances is available in the energy arrays surrounding organisms, and this information is detected by organisms in order to perceptually guide their actions. At the behavioral scale, organisms responding to affordances are understood as self-organizing and reorganizing softly-assembled synergies. Within the ecological community, little effort has so far been devoted to studying this process at the neural scale, though interest in the topic is growing under the header of ecological neuroscience. From this perspective, switches between affordances may be conceptualized as transitions within brain-body-environment systems as a whole rather than under the control of a privileged (neural) scale. We discuss extant empirical research at the behavioral scale in support of this view as well as ongoing and planned work at the neural scale that attempts to further flesh out this view by characterizing the neural dynamics that are associated with these transitions while participants dynamically respond to affordances.
Frontiers in Psychology: Theoretical and Philosophical Psychology, 2022
Mainstream cognitive neuroscience aims to build mechanistic explanations of behavior by mapping a... more Mainstream cognitive neuroscience aims to build mechanistic explanations of behavior by mapping abilities described at the organismal level via the subpersonal level of computation onto specific brain networks. We provide an integrative review of these commitments and their mismatch with empirical research findings. Context-dependent neural tuning, neural reuse, degeneracy, plasticity, functional recovery, and the neural correlates of enculturated skills each show that there is a lack of stable mappings between organismal, computational, and neural levels of analysis. We furthermore highlight recent research suggesting that task context at the organismal level determines the dynamic parcellation of functional components at the neural level. Such instability prevents the establishment of specific computational descriptions of neural function, which remains a central goal of many brain mappers – including those who are sympathetic to the notion of many-to-many mappings between organismal and neural levels. This between-level instability presents a deep epistemological challenge and requires a reorientation of methodological and theoretical commitments within cognitive neuroscience. We demonstrate the need for change to brain mapping efforts in the face of instability if cognitive neuroscience is to maintain its central goal of constructing computational mechanistic explanations of behavior; we show that such explanations must be contextual at all levels.
Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways ... more Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15 (1), 20–25] proposal to distinguish the dorsal and ventral systems on basis of the functional demands they serve (i.e., action and perception), a vast literature has emerged that scrutinized if the dorsal and ventral systems indeed process information into egocentric and allocentric codes in accordance with their respective functions. However, a corollary of Goodale and Milner’s original proposal, that these functional demands also impose different constraints on information detection, has been largely overlooked. In the present study, we measured gaze patterns to investigate how information detection for action and perception differs. In two conditions, participants (N=9) grasped or made a manual estimate of the length of a shaft embedded in a Müller-Lyer configuration. The illusion significantly affected the manual estimates, but not...
Limb apraxia is evident in approximately 50% of patients after left hemisphere cerebral vascular ... more Limb apraxia is evident in approximately 50% of patients after left hemisphere cerebral vascular accident (LCVA) and increases disability and caregiver dependence. Individuals with apraxia exhibit abnormalities in spatio-temporal aspects of gesture production and/or in knowledge of tool-related actions (action semantics). This preliminary study of three LCVA participants aimed to (i) explore the efficacy of a novel Action Network Treatment (ANT) that focused on improving the semantic association between tool actions and other types of tool knowledge, an intervention inspired by successful semantic network treatments in aphasia (e.g., Edmonds et al., 2009), and (ii) explore whether there are individuals with apraxia who benefit from ANT relative to a version of a comparatively well-studied existing apraxia treatment (Smania et al., 2006; Smania et al., 2000) that shapes gesture via focus on practicing the spatio-temporal aspects of gesture production (Tool Use Treatment or TUT). One participant demonstrated treatment benefits from both ANT and TUT, while another only benefited from TUT. These findings indicate that our novel semantic network strengthening approach to gesture training may be efficacious in at least some individuals with apraxia, and provide a foundation for future study of the characteristics of people with apraxia who benefit from each approach.
Modulation of excitability in the motor system can be observed before overt movements but also in... more Modulation of excitability in the motor system can be observed before overt movements but also in response to covert invitations to act. We asked whether such changes can be induced in the absence of even covert motor instructions, namely, as a function of the location of the hand with reference to the body. Participants received single-pulse TMS over the motor cortex while they placed their contralateral hand (right hand in Experiment 1, left hand in Experiment 2) to the right or left of their body midline, and looked either at or away from their hand. In both experiments, greater excitability was observed when gaze was directed to the right. This finding is interpreted as a consequence of left brain later- alization of motor attention. Contrary to our expectations, we furthermore consistently observed greater excitability when gaze was directed away from the hand. To account for this finding, we introduce the concept of “surveillance attention” which, we speculate, modulates cortical gain, and thereby cortical excitability. Its function is to increase read- iness to act in non-foveated regions of space. Such a process confers an advantage in environments, like those in which humans evolved, in which threatening stimuli may appear unexpectedly, and at any time.
Ecological psychology has been criticized for ignoring the brain in its theory formation. In rece... more Ecological psychology has been criticized for ignoring the brain in its theory formation. In recent years, however, a number of researchers have started asking ecologically-inspired questions about the ways in which not only the embodied activity of the organism in its environment, but also the particulars of the organism's nervous system matter. This work has typically appeared in neuroscience journals, thereby potentially escaping the attention of ecological psychologists. The current article introduces a Special Issue of Ecological Psychology that aims to correct this problem. This Issue brings together one empirical and six theoretical articles that develop ideas about the contributions of the nervous system to perception-action. We briefly review each of the articles, identify common themes, and point out the surprising variety in theoretical positions. It is hoped that this Special Issue will help guide discussions amongst ecological psychologists and (ecological) neuroscientists as they confront the question “What should a ‘Gibsonian neuroscience’ look like?”
Rahnev and Denison addressed the issue of (sub)optimalities in perception but only made a passing... more Rahnev and Denison addressed the issue of (sub)optimalities in perception but only made a passing reference to evolutionary thinking. In our commentary, we concur with the authors' claim that evolution does not work towards optimalities, but argue that an evolutionary perspective on perception questions the Bayesian approach that the authors adopted.
Objectives: Adaptive interaction with the environment requires the ability to predict both human ... more Objectives: Adaptive interaction with the environment requires the ability to predict both human and non-biological motion trajectories. Prior accounts of the neurocognitive basis for prediction of these two motion classes may generally be divided into those that posit that non-biological motion trajectories are predicted using the same motor planning and/or simulation mechanisms used for human actions, and those that posit distinct mechanisms for each. Using brain lesion patients and healthy controls, this study examined critical neural substrates and behavioral correlates of human and non-biological motion prediction. Methods: Twenty-seven left hemisphere stroke patients and 13 neurologically intact controls performed a visual occlusion task requiring prediction of pantomimed tool use, real tool use, and non-biological motion videos. Patients were also assessed with measures of motor strength and speed, praxis, and action recognition. Results: Prediction impairment for both human and non-biological motion was associated with limb apraxia and, weakly, with the severity of motor production deficits, but not with action recognition ability. Furthermore, impairment for human and non-biological motion prediction was equivalently associated with lesions in the left inferior parietal cortex, left dorsal frontal cortex, and the left insula. Conclusions: These data suggest that motor planning mechanisms associated with specific loci in the sensorimotor network are critical for prediction of spatiotemporal trajectory information characteristic of both human and non-biological motions. (JINS, 2017, 23, 171–184)
Gibson argued that illusory pictorial displays contain "inadequate" information (1966, p. 288) bu... more Gibson argued that illusory pictorial displays contain "inadequate" information (1966, p. 288) but also that a "very special kind of selective attention" (p. 313) can dispel the illusion—suggesting that adequate perceptual information could in fact be potentially available to observers. The present paper describes Gibson's treatment of geometrical illusions and reviews pertinent empirical evidence. Interestingly, Gibson's insights have been corroborated by recent findings of inter- and intra-observer variability in susceptibility to visual illusions as a function of culture, learning and task. It is argued that these findings require a modification of the general Gibsonian principle of perception as the detection of specifying information. Withagen and Chemero's (2009) evolutionary motivated reconceptualization of perception predicts observers' use of both specifying and non-specifying information and inter- and intra-observer variability therein. Based on this reconceptualization we develop an ecological approach to visual illusions that explains differential illusion effects in terms of the optical variable(s) detected.
The dominant view of the ventral and dorsal visual systems is that they subserve perception and a... more The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters (2011) suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching (perception), pointing (action) and perceptual judgment responses to masked Müller–Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length at brief durations remained sensitive to veridical stimulus length (egocentric information), but not the illusion (allocentric, context-dependent information), which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception (matching) or action (pointing) responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric and slower allocentric information pick up, respectively.
There is ongoing debate with respect to interpretation of the finding that, in contrast to percep... more There is ongoing debate with respect to interpretation of the finding that, in contrast to perceptual size judgments, actions are relatively unaffected by the Müller–Lyer illusion. In normal unrestricted viewing situations observers cannot perform an action directed at an object without simultaneously perceiving the object – this makes it difficult to unequivocally establish whether observed effects are a function of vision for perception, vision for action, a combination of both, or of a single all-purpose visual system. However, there is evidence that observers are capable of performing actions towards objects of which they are not consciously aware, implying that two distinct visual thresholds may exist; one accompanying vision for action and one accompanying vision for perception. To investigate this possibility we created a situation in which visual information was presented below the perception threshold, but above the purported action threshold, allowing examination of action responses independent of contributions from vision for perception. Following a perceptual categorization task, participants performed delayed pointing movements towards briefly exposed masked Müller–Lyer targets of different sizes. When the targets were presented below the perception threshold, participants were unable to discriminate between them, yet their delayed pointing movements were affected by target size (but not the illusion). The results imply that vision for action is functional even after a delay and/or that the pickup of egocentric information is associated with a lower visual threshold than the pickup of allocentric information.
Based upon evidence that vision for action has quicker access to visual information than vision f... more Based upon evidence that vision for action has quicker access to visual information than vision for perception, we hypothesized that the two systems may have differentiated visual thresholds. There is also evidence that, unlike vision for perception, vision for action is insensitive to cognitive dual-task interference. Using visual masking, we determined the visual thresholds of 15 participants in a perception task, an action task and an action plus concurrent cognitive secondary task. There was no difference in threshold between the perception task and the action task, but the action plus concurrent secondary task was accompanied by a greater visual threshold than both the perception task and the action task alone, indicating dual-task interference. The action task was thus most likely informed by vision for perception. The implications of these results are reviewed in the context of recent discussions of the two visual systems model.
Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways ... more Following Goodale and Milner’s [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15 (1), 20–25] proposal to distinguish the dorsal and ventral systems on basis of the functional demands they serve (i.e., action and perception), a vast literature has emerged that scrutinized if the dorsal and ventral systems indeed process information into egocentric and allocentric codes in accordance with their respective functions. However, a corollary of Goodale and Milner’s original proposal, that these functional demands also impose different constraints on information detection, has been largely overlooked. In the present study, we measured gaze patterns to investigate how information detection for action and perception differs. In two conditions, participants (N=9) grasped or made a manual estimate of the length of a shaft embedded in a Müller-Lyer configuration. The illusion significantly affected the manual estimates, but not the hand aperture during grasping. In line with these behavioral findings, significant differences in gaze patterns were revealed between the two tasks. Participants spent more time looking at areas that contain egocentric information (i.e., centre of the shaft) when grasping as compared to making a manual length estimate. In addition, participants, made more gaze shifts (i.e., especially between the two areas surrounding the shaft endpoints and including the arrowheads) when making the manual length estimate, enabling the pick up of allocentric information. This difference was more pronounced during task execution as compared to task preparation (i.e., before movement onset). These results support the contention that the functional distinction between the dorsal and ventral systems is not limited to the processing of information, but also encompasses the detection of information.
In the present study, we examined whether individual differences in the perception of illusory Ju... more In the present study, we examined whether individual differences in the perception of illusory Judd drawings point to variability in the pickup of informational variables. Two sources for these individual differences were addressed: culture and learning. East Asian (n = 24) and Western (n = 24) participants made perceptual judgments of the midpoint of the shaft of various Judd figures in a pretest–practice–posttest design. During practice, half of the participants received feedback about the actual midpoint after each trial, while the other half did not receive feedback. The results showed differences among perceivers of different cultures in judging the midpoints of the shafts of Judd figures, particularly with respect to their propensity to improve perceptual accuracy after repeated practice and feedback. For most participants, changes in illusory bias as a consequence of learning were shown to reflect either a change in what informational variable they exploited or a rescaling or calibration of the perception to the informational variable. However, the individual differences in illusory bias related to culture could not be unequivocally attributed to either of these perceptual-learning processes.
Avant: Journal of the Philosophical-Interdisciplinary Vanguard , 2012
Gibson developed the affordance concept to complement his theory of direct perception that stands... more Gibson developed the affordance concept to complement his theory of direct perception that stands in sharp contrast with the prevalent inferential theories of perception. A comparison of the two approaches shows that the distinction between them also has an ontological aspect. We trace the history and newer formalizations of the notion of affordance and discuss some competing opinions on its scope. Next, empirical work on the affordance concept is reviewed in brief and the relevance of dynamical systems theory to affordance research is demonstrated. Finally, the striking but often neglected convergence of the ideas of Gibson and those of certain Continental philosophers is discussed.
We investigated whether the control of movement of the left hand is more likely to involve the us... more We investigated whether the control of movement of the left hand is more likely to involve the use of allocentric information than movements performed with the right hand. Previous studies (Gonzalez et al. in J Neurophys 95: 3496–3501, 2006; De Grave et al. in Exp Br Res 193: 421–427, 2009) have reported contradictory findings in this respect. In the present study, right-handed participants (N=12) and left-handed participants (N=12) made right-and left-handed grasps to foveated objects and peripheral, non-foveated objects that were located in the right or left visual hemifield and embedded within a Müller-Lyer illusion. They were also asked to judge the size of the object by matching their hand aperture to its length. Hand apertures did not show significant differences in illusory bias as a function of hand used, handedness or visual hemifield. However, the illusory effect was significantly larger for perception than for action, and for the non-foveated compared to foveated objects. No significant illusory biases were found for reach movement times. These findings are consistent with the two-visual system model that holds that the use of allocentric information is more prominent in perception than in movement control. We propose that the increased involvement of allocentric information in movements toward peripheral, non-foveated objects may be a consequence of more awkward, less automatized grasps of nonfoveated than foveated objects. The current study does not support the conjecture that the control of left-handed and right-handed grasps is predicated on different sources of information.
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