The Organization of Visually Mediated Actions in a Subject without Eye Movements

Abstract

We investigated the visual strategy of a subject without eye movements (AI), comparing her with normal subjects on the 'real-life' task of making a cup of tea. Differences in overall performance were surprisingly few. She took no more time than the controls to complete the tea-making task and the division of the task into object-related actions was essentially similar. However, the way AI took in visual information was very different from the normal subjects who used a typical 'saccade and fixate' strategy when moving between and scrutinizing objects. AI made saccades with the head, which were on average 1.5 times larger than the eye-head saccades of the controls and lasted four times as long, meaning that AI would have had impaired vision for more of the time than the controls. She also made only approximately one-third as many saccades as normals during the same task. However, she had another strategy, 'slow drift', in which she allowed her eyes to move smoothly across the scene at speeds of up to 30 degrees /s. Such movements were never seen in the controls, and we assume that AI used them to offset the cost in time of the slow head saccades, even though they had their own cost in terms of reduced resolution. We demonstrate that these differences have a minimal effect on the timings of events during an object-related action. We discuss supervisory checking operations within actions, and consider what information is needed for appropriate gaze control during object-related actions.

Balancing energetic and cognitive resources: Memory use during search depends on the orienting effector

“…First, we note that for the range of gaze shift eccentricities in the present study, head movements have previously been reported to be between 4 and 10 times slower than corresponding eye movements (Zangemeister & Stark, 1981). However, from our results, during random trials head-contingent search was only about 1.5 times slower, and actually exhibited a shallower slope than eye-contingent search, suggesting that -like oculomotor paralysis patients who cannot use eye movements (Land, Furneaux, & Gilchrist, 2002) -head-contingent searchers already compensate for their time delays by searching more efficiently.…”

From Exploration to Fixation: An Integrative View of Yarbus’s Vision

“…These head saccades enabled the patient to read at normal speed and even carry out complex visuomotor tasks, such as making a cup of tea, without problems. The authors concluded that ''saccadic movements, of the head or the eye, form the optimal sampling method for the brain'' (compared with smooth scanning of the visual scene; Gilchrist et al, 1997;Gilchrist, Brown, Findlay, & Clarke, 1998;Land, Furneaux, & Gilchrist, 2002).…”

Search training for people with visual field loss after stroke: A cohort study

“…Another aspect of this modelling process is to determine the mechanisms by which the intervention works; in this case, how participants’ search and scanning behaviour is changed as a result of the intervention. Methods for measuring patients’ behaviours while searching real environments are not well developed, though this has been done in healthy subjects (Land et al., 1999) and in a single case study (Land et al., 2002). Visual exploration of scenes in the real world involve not only eye but also head and whole body movements, particularly when shifting the point of gaze by more than 10 degrees of visual angle (Freedman, 2008; Guitton and Volle, 1987; Land et al., 1999).…”

“…Methods for measuring patients’ behaviours while searching real environments are not well developed, though this has been done in healthy subjects (Land et al., 1999) and in a single case study (Land et al., 2002). Visual exploration of scenes in the real world involve not only eye but also head and whole body movements, particularly when shifting the point of gaze by more than 10 degrees of visual angle (Freedman, 2008; Guitton and Volle, 1987; Land et al., 1999). A method for measuring where the person is looking with respect to a scene would potentially provide information about how an intervention works.…”