Introduction and background information
For decades, the field of visual perception has received considerable attention from scholars, experts, and other stakeholders. As such, research has been carried out to investigate visual mechanisms and visual control actions in human beings and other animals, especially primates (Goodlade & Milner 1992; Schenk 2012; Mishkin, Ungerleider & Macko1983). One of the key areas of focus pertains to action and perception. While some scholars and/or researchers report separation between action and perception, others propose that there are considerable interactions and coupling between the two mechanisms (Schenk 2012; Mishkin, Ungerleider & Macko 1983; Schenk & McIntosh 2010; Pretegiani et al. 2015).
This paper critically reviews the article by Goodlade and Milner (1992). The study proposed that “the ventral stream of projections from the striate cortex to the inferotemporal cortex plays the major role in the perceptual identification of objects, while the dorsal stream projecting from the striate cortex to the posterior parietal region mediates the required sensorimotor transformations for visually guided actions directed at such objects” (Goodlade & Milner 1992, p. 20). As such, two distinct mechanisms separate action and perception.
The contextual review seeks to establish the contribution, findings, and their implications, methodology, and limitation of the article. It is worth noting that new developments have been made since the publication of the article. As such, the review also seeks to establish how the article fits in the recent findings in the visual perception field.
The argument and findings before and in the early 1990s
To appreciate the historical context of the publication of the article by Goodlade and Milner (1992), it is prudent to discuss what was happening before and in the early 1990s in the field of visual perception.
Goodlade and Milner (1992) introduced the article by discussing what they considered the inception of the dual representations of visual mechanisms. As such, the author sought for publications made in slightly above two decades in the field. The first article considered by Goodlade and Milner (1992) is a then influential article by Schneider (1969), which was considered a breakthrough in the research on the separation of pathways in visual perception. Schneider (1969) hypothesized anatomical dissociation between visual coding of object location and identification to depart from the monolithic portrayal and comprehension of the visual function (Goodlade & Milner 1992). Stimuli location was attributed to the retinotectal pathway while identification was accredited to the then-novel geniculostriate system (Goodlade & Milner 1992).
Although part of the hypothesis by Schneider (1960) was disputed and disregarded by later research (Goodlade & Milner 1992), Schneider made vital contributions in the distinction between object identification and spatial localization, which formed the basis of subsequent research in the field of visual perception (Goodlade & Milner 1992). Therefore, Goodlade and Milner (1992) sought for publications that developed on the separation of visual pathways as postulated by Schneider (1962).
Goodlade and Milner (1992) adopted an article authored by Mishkin, Ungerleider, and Macko (1983), which they considered relevant and quite informative since they had based their study on separation of visual pathways. Mishkin, Ungerleider, and Macko (1983) made a key contribution by providing the inference that appreciation of stimuli’s qualities and their spatial location are attributed to interpretation of information in distinct mechanisms, including inferior temporal for qualities and posterior parietal cortex for spatial location (Goodlade & Milner 1992; Mishkin, Ungerleider & Macko 1983). The pertinence and reliability of the conclusion by Mishkin, Ungerleider, and Macko (1983) were enhanced by the fact that they adopted authentic anatomical and behavioral research publications and empirical studies on lesions. Further, their studies revealed there are links between profound impairment in visual pattern discrimination/recognition and inferotemporal cortex (with less impairment in working out on landmark tasks) (Goodlade & Milner 1992; Mishkin, Ungerleider & Macko 1983). On posterior parietal lesions, divergent results were observed. Therefore, Mishkin, Ungerleider, and Macko (1983) concluded that while posterior partial lesions interrupted spatial perception, inferotemporal lesions hampered stimuli’ identification (Goodlade & Milner 1992; Mishkin, Ungerleider & Macko 1983).
It is worth noting that after the publication of Mishkin, Ungerleider, and Macko (1983) and before Goodlade and Milner (1992), there was significantly huge research and implications in the field, including the studies on ‘parvo’ and ‘Magno’ subdivisions in visual pathways (Goodlade & Milner 1992).
Decisively, the article by Goodlade and Milner (1992) fits in the research before and in the early 1990s. The study developed on prior publications such as Schneider 1969 and Mishkin, Ungerleider, and Macko (1983), which emphasized the separation of pathways. Goodlade and Milner (1992) provide more insight into the separation of pathways, especially on perception and action.
Recent findings
Research on visual perception is progressive. Post-1990 studies have either developed the Goodlade and Milner (1992) model or posed considerable levels of challenge(Schenk 2012; Milner & Goodale 2008; Schenk & McIntosh 2010).
Schenk and McIntosh (2010) appreciate the considerable progress of the perception-action model in the visual perception field. The article critically reviews the literature on the field paying attention to the development, contentions, and support for the perception-action model in the 1990s and the early 21st century. The model proposed by Goodlade and Milner (1992) has had a considerable influence by providing a unifying and plausible account in the visual perception field (Schenk & McIntosh 2010). The article termed the model by Goodlade and Milner (1992) to have a conceptual simplicity and counterintuitive appeal, which have created dissemination and discussion not only in cognitive neuroscience and visual perception but also in other fields (Schenk & McIntosh 2010). As such, the assumptions/findings/implications by Goodlade and Milner (1992) as presented in the perception-action model have been the focus of numerous empirical research works (Schenk & McIntosh 2010).
Schenk and McIntosh (2010) found mixed evidence for the model’s specific claims, more so in the high degree of common exclusivity in the two visual mechanisms. The paper, therefore, gives mixed judgment on the perception-action model by Goodlade and Milner (1992) terming the characterizations as partly (broadly) accurate, but the specialization still lacks absolute accuracy.
Schenk and McIntosh (2010) upheld the significance of the ventral stream mechanism for stimuli’ comprehension and its involvement in forging the context in awareness. Moreover, the functioning of the dorsal stream in guiding action was appreciated and considered vital. Schenk and McIntosh (2010) termed the two functions by the two visual mechanisms as secure. Nevertheless, the authors cast some doubts on the common exclusivity in the domains related to perception and action.
The article had different sections with different conclusions. The determination in section 2 in the article proposed that the effects of the ventral system on action are unlimited to high degree planning echelons rather they are extended to the spatial programming of low-degree action levels. On the other hand, Section 6 suggested that dorsal visual mechanisms add egocentric spatial characteristics to the visual awareness having straight involvement in perception. For sections 3 and 5, a considerable proof was established that proposed that the ventral stream was exclusively responsible for encoding allocentric associations between stimuli or back sustained visual representations. Contrariwise, the data suggests that the dorsal stream can access and employ ventrally derived visual representations. As such, suggestions supporting the inter-stream interactions are emphasized. Consequently, the recurrent theme of the present review on the visual streams and other sections of the brain working together is emphasized.
For instance, on the hypothetical ground that the exclusive role is of the ventral stream in visual awareness provision is accepted, stimuli awareness would necessitate attentional modulation from other brain sections. It could also be argued that descriptive labeling on perception and/or action should not be done on particular involvement of any sub-division of the entire involved networking system.
The essence of the model by Goodlade and Milner (1992) was to move away from the classical conception of unitary visual representation. Possibly, different roles played by the two visuals have been overemphasized at the expense of interactions evident between them.
Schenk (2012) made a significant finding of the model proposed by Goodlade and Milner (1992). The author examined the grasping mechanism in a patient using a mirror to establish the dissociation between the images of a stimulus from its physical presence. Normalcy was only evident when the patient received haptic feedback. As such, DF can depend on haptic feedback to compensate for the inability to perceive the size of a stimulus. This provides a significant elucidation on why the patient had better grasping relative to her perception. Therefore, the inter-stream interactions are further highlighted.
Conclusively, it is evident that Goodlade and Milner (1992) identify with the findings from 1992 onwards where immense research has been done in the field. Considerable research has been based on the perception-action model proposed by Goodlade and Milner (1992) where the model has been supported or challenged.
Methodology
The article adopted the approach of ‘what’ versus ‘how’ in the dichotomy between ventral and projection emphasizing output requirement (Goodlade & Milner 1992).
Particularly, a study of a DF patient who had recovered from Balint’s syndrome, characterized by considerable “bilateral parietal damage and profound disorder of spatial attention gaze and visually guided reaching” (Goodlade & Milner 1992, p. 21). Although the patient could easily recognize line drawings in regular objects, she demonstrated impairment in picking the objects (Goodlade & Milner 1992; Schenk 2012).
For instance, when the patient attempted to grasp small objects (with differences in sizes from each attempt) she erred relating the magnitude of the opening between grasping fingers and the specific size of an object. In addition to her inability to demonstrate normal scaling in grasping movements, the patient made several adjustments in her grasp as she moved her hand closer to the objects, which is quite abnormal (Goodlade & Milner 1992).
The study established that grasping depended on a distinct representation of visual size in the dorsal stream and did not necessitate visual input from the ventral stream (Schenk 2012; Goodlade & Milner 1992).
Contributions and the implications of the findings
Goodlade and Milner (1992) made a significant contribution in departing from the monolithic portrayal and comprehension of the visual function. Initially, the visual perception was understood to have a monolithic, unitary, and all-purpose mechanism (Schenk & McIntosh 2010; Goodlade & Milner 1992; Mishkin, Ungerleider & Macko 1983).
Goodlade & Milner (1992) endeavored to displace this notion marshaling their support from earlier finding and implications, such as findings by Schneider (1969), Mishkin, Ungerleider, and Macko (1983), research done from 1983 to early 1990s, and the study on a DF patient. The study implications suggested dissociations between perception and action. The vision-for-perception and the vision-for-action model were consequently proposed.
As mentioned earlier, the model has been the target for many studies where development, support, and challenge for the model have been made.
Limitations
Although the article by Goodlade and Milner (1992) made considerable contributions and breakthroughs in the field of visual perception, it has been challenged by numerous studies. Researchers have flawed some of the implications and the findings, especially on the relationship between dorsal and the ventral stream. The model proposed by (Goodlade & Milner 1992) is said to be limited and lacking absolute accuracy due to the overemphasizing the independent roles the two visual mechanisms play at the expense of their evident interaction in visual representation.
Conclusion
It is imperative to note that the article is a vital publication in the field of visual representation. The paper fits in the findings established before and after the early 1990s, especially by Schneider (1969) and Mishkin, Ungerleider, and Macko (1983). Further, the paper adopted an empirical study, a plausible methodology, and pertinent research to come up with vital contributions that separated the perception and action pathways. Recent research has made a significant attempt to uphold or challenge the model by Goodlade and Milner (1992). As such, the model has been supported and developed further. However, some aspects such as overlooking the vital interactions between the dorsal and the ventral streams have been greatly challenged.
References
Goodlade, MA & Milner, D 1992,’Separate visual pathways for perception and action’, TINS, vol.15, no. 1, pp. 20-25.
Milner, AD & Goodale, MA 2008, ‘Two visual systems re-viewed’,Neuropsychologia, vol. 46, no. 2008, pp. 774-778.
Mishkin, M, Ungerleider, LG & Macko, KA 1983,’Object visual and spacial visual: two cortical pathways’, TINS, pp. 414-417.
Pretegiani, E, Astefanoaei, C, Daye, MP, FitzGibbon, EJ, Creanga, D-E, Rufa, A & Optican, ML 2015,’Action and perception are temporally coupled by a common mechanism that leads to a timing misperception’,Journal of Neuroscience, vol.35, no. 4, pp. 1493-1504.
Schenk, T 2012,’No dissociation between perception and action in patient DF when haptic feedback is withdrawn’,Journal of Neuroscience, vol. 32, no. 6.
Schenk, T & McIntosh, R n.d.,’Do we have independent visual streams for perception and action?. pp. 1-44.