Vision And Action PDF

VISION AND ACTION 1  What is the purpose of vision? 2  What is the purpose of vision? Gibson (1979, p. 239) argued that perception involves “keeping in touch with the environment”. 3 Dire...

VISION AND ACTION 1  What is the purpose of vision? 2  What is the purpose of vision? Gibson (1979, p. 239) argued that perception involves “keeping in touch with the environment”. 3 Direct perception Developed by Gibson (1950, 1966, 1979) There is more to perception than object identification Perception and action are closely intertwined We can relate Gibson’s views to Milner and Goodale’s (1995, 2008) vision-for-action system (see Chapter 2). According to both theoretical accounts, there is an intimate relationship between perception and action. An ecological approach in his direct theory of perception Information pickup from the ambient optic array The pattern of light reaching the eye Provides unambiguous information about object layout This occurs without much information processing 4 Optic flow Gibson produced training lms in the Second World War describing how pilots handle taking off and landing. Of crucial importance is optic ow – the changes in the pattern of light reaching observers when they move or parts of the visual environment move. When pilots approach a landing strip, the point towards which they are moving (focus of expansion) appears motionless with the rest of the visual environment apparently moving away from that point. The further away any part of the landing strip is from that point, the greater is its apparent speed of movement. Changes in the pattern of light Optic flow field as a pilot comes in to land, with the focus of expansion (point towards which the pilot is heading) in the middle (From Gibson, 1950, Wadsworth, a part of Cengage Learning, Inc. ) 35 fi fl  Optic flow Optic ow has several functions for behaving observers (see, e.g., Lee, 1980): For instance, observers can perceive their direction of self-motion from optic ow (Gibson, 1947, 1950; Warren, 1976; Warren et al., 1988; see Warren, 2008 for a review), and optic ow provides visual guidance for many actions (Warren, 1998, 2021) such as steering to a target (Calvert, 1954; Gibson, 1958; Warren et al., 2001), balance and posture control (Lee & Aronson, 1974; Stoffregen, 1985) and avoiding or achieving collisions (Fajen, 2008; Lee, 1976). Optic ow furthermore plays an important role in the perception of the shape of objects and the layout of the environment (Koenderink, 1986; Rogers, 2021; Todd, 1995) 6 fl fl fl fl Affordances According to Gibson (1979), the potential uses of objects (their affordances) are directly perceivable. For example, a ladder “affords” ascent or descent. Gibson believed that “affordances are opportunities for action that exist in the environment and do not depend on the animal’s mind... they do not cause behaviour but simply make it possible” (Withagen et al., 2012, p. 251). In Gibson (1979, p. 127), affordances are what the environment “offers the animal, what it provides or furnishes”. Perception and action are tightly linked: objects may be perceived not only in terms of visual features, but also in terms of possibilities for action. 7 Affordances (Pappas & Mack, 2008) The response side primed by the object affordance was either congruent or incongruent with the side required by a following button press. 8  Affordances (Wilf et al. 2013) Wilf et al. (2013) focused on the affordance of graspability with participants lifting their arms to perform a reach-like movement with graspable and non-graspable objects Muscle activity (EMG* signal) started faster for graspable than non-graspable objects suggesting that the affordance of graspability triggers rapid activity in the motor system. *Electromyography (EMG) is a technique for (From Wilf et al., 2013, evaluating and recording the electrical activity Frontiers in Psychology) produced by skeletal muscles. 9 Direct perception: evaluation Strengths Limitations Emphasised ecological validity Processes involved in Noted the informational perception are much richness contained within more complicated and visual stimuli “cognitive” than implied by Gibson Emphasised importance of motion in perception Ignoring internal and disagreed with studying representations to static observers viewing static understand perception displays was a serious flaw Underestimated the Anticipated future importance of top-down developments processes (e.g., based on (e.g., vision-for-action system knowledge) of Milner & Goodale, 1995; 2008) Oversimplified the role of motion on perception 10 How do we perform successful goal directed actions towards objects? 11 Planning-control model (Glover, 2004) Planning system Mostly used before initiation of movement Selects an appropriate target Decides how the object will be grasped Determines the timing of the movement Uses both spatial and non-spatial information Relatively slow Planning depends on: A visual representation in the inferior parietal lobe Motor processes in the frontal lobes + basal ganglia 12 Planning control model Control system Used after the planning system To ensure that movements are accurate Actual movement compared with desired movement Proprioception is involved Influenced by the target object’s spatial characteristics Relatively fast Control depends on: A visual representation in superior parietal lobe Motor processes in the cerebellum 13 Planning control model According to the planning-control model, various factors (e.g., semantic properties of the visual scene) influence the planning process associated with goal-directed movements but not the subsequent control process. This prediction was tested by Namdar et al. (2014). Participants grasped an object in front of them using their thumb and index finger. The object had a task-irrelevant digit (1, 2, 8 or 9) on it. As predicted, numerically larger digits led to larger grip apertures during the first half of the movement trajectory but not the second half (involving the control process). 14 Planning control model: evaluation Strengths Some evidence of successive planning and control stages Largely separate brain areas involved in planning and control Support for cognitive processes in planning 15 Two Dorsal Visual Streams Actions can involve: (1) dorso-dorsal stream (“grasp” system rapidly using accessible object properties (e.g., size, shape) (2) ventro-dorsal stream (“use” system slowly using memorised object knowledge (Sakreida et al., 2016) (Sakreida et al., 2016, Elsevier) 16  Two Dorsal Visual Streams Evidence from brain-damaged patients is also supportive of the distinction between two dorsal streams. Patients with damage to the ventro-dorsal stream. Much research has focused on limb apraxia, a disorder where patients often fail to make precise goal-directed actions in spite of possessing the physical ability to perform those actions (Pellicano et al., 2017). More specifically, “Reaching and grasping actions in LA [limb apraxia] are normal when vision of the limb and target is available, but typically degrade when they must be performed ‘off-line’, as when subjects are blindfolded prior to movement execution” (Binkovski & Buxbaum, 2013, p. 5). This pattern of findings is expected if the dorso-dorsal stream is intact in patients with limb apraxia. Patients with damage to the dorso-dorsal stream. Much research here has focused on optic ataxia. As predicted, patients with optic ataxia have impaired online motor control and so exhibit inaccurate reaching towards (and grasping of) objects. 17