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Biomedical subjects

Michael F Land

Publications and source records attributed to Michael F Land.

13 recordsLinked to original sources
PubMed2006

Eye movements and the control of actions in everyday life.

The patterns of eye movement that accompany static activities such as reading have been studied since the early 1900s, but it is only since head-mounted eye trackers became available in the 1980s that it has been possible to study active tasks such as walking, driving, playing ball games and ordinary everyday activities like food preparation. This review examines the ways that vision contributes to the organization of such activities, and in particular how eye movements are used to locate the information needed by the motor system in the execution of each act. Major conclusions are that the eyes are proactive, typically seeking out the information required in the second before each act commences, although occasional 'look ahead' fixations are made to establish the locations of objects for use further into the future. Gaze often moves on before the last act is complete, indicating the presence of an information buffer. Each task has a characteristic but flexible pattern of eye movements that accompanies it, and this pattern is similar between individuals. The eyes rarely visit objects that are irrelevant to the action, and the conspicuity of objects (in terms of low-level image statistics) is much less important than their role in the task. Gaze control may involve movements of eyes, head and trunk, and these are coordinated in a way that allows for both flexibility of movement and stability of gaze. During the learning of a new activity, the eyes first provide feedback on the motor performance, but as this is perfected they provide feed-forward direction, seeking out the next object to be acted upon.

Activities of Daily Living↗
PubMed2005

Eye-hand coordination: learning a new trick.

In many manual tasks, a specific repertoire of eye movements accompanies the actions. A new study has shown how this pattern changes as eye and hand become coordinated when learning a new skill.

Eye Movements↗
PubMed2005

Different retina-lamina projections in mosquitoes with fused and open rhabdoms.

Anopheles gambiae and Toxorhynchites brevipalpis represent the nocturnal and diurnal extremes of the mosquito light intensity range, and their eyes are structurally very different. A. gambiae has fused rhabdoms with huge acceptance angles, whereas T. brevipalpis has open rhabdoms with rhabdomere acceptance angles comparable with those of advanced (brachyceran) flies. Here, we show that the retina-lamina projections are consistent with these differences. The short receptor axons from each ommatidium in A. gambiae insert as a group between four lamina monopolar cell clusters. In T. brevipalpis axon bundles from each ommatidium undergo a twist in their passage through the nuclear layer of the lamina, and then fan out into a space the diameter of which is about twice the separation of the monopolar cell clusters. This arrangement is consistent with a neural superposition mechanism closely similar to that found in higher Diptera, but which must have evolved independently.

Animals↗
PubMed2005

Visual memory for objects in natural scenes: from fixations to object files.

Object descriptions are extracted and retained across saccades when observers view natural scenes. We investigated whether particular object properties are encoded and the stability of the resulting memories. We tested immediate recall of multiple types of information from real-world scenes and from computer-presented images of the same scenes. The relationship between fixations and properties of object memory was investigated. Position information was encoded and accumulated from multiple fixations. In contrast, identity and colour were encoded but did not require direct fixation and did not accumulate. In the current experiments, participants were unable to recall any information about shape or relative distances between objects. In addition, where information was encoded we found differential patterns of stability. Data from viewing real scenes and images were highly consistent, with stronger effects in the real-world conditions. Our findings imply that object files are not dependent upon the encoding of any particular object property and so are robust to dynamic visual environments.

Adult↗
PubMed2004

Nocturnal vision: bees in the dark.

Some eyes work better in the dark than others. The apposition type of compound eye that bees and other diurnal insects possess is usually of little use after nightfall. Nevertheless some tropical sweat bees have pushed the limits of this unfavourable design so far that they can navigate using landmarks that are too dim for humans to make out.

Animals↗
PubMed2004

The coordination of rotations of the eyes, head and trunk in saccadic turns produced in natural situations.

In real life situations large gaze saccades may involve rotations of the trunk, as well as the eyes and head. When this happens the rotation of the head-in-space is similar whether or not the trunk is also rotating. However, the rotation of the head on the trunk (i.e. the neck movement) is very different in the two circumstances. For similar head-in-space rotations to occur, the neck and trunk movements cannot simply add independently: they must be coordinated. It is argued that this is achieved via a feedback loop in which the semi-circular canals monitor the rotation of the head-in-space, and the neck is driven by an error signal representing the difference between the intended head-in-space trajectory and the actual trajectory. This mechanism, which is essentially the same as the vestibulo-collic reflex, nulls out disturbances to the head-in-space trajectory, whether these are caused by active or passive trunk rotation.

Abdomen↗
PubMed2003

Colour vision: colouring the dark.

Humans lose colour vision at night and it has often been assumed that this happens to other animals as well. It is not true of nocturnal moths, however: a recent study has shown that the elephant hawk moth makes use of trichromatic colour vision when seeking flowers by starlight.

Animals↗
PubMed2003

The spatial resolution of the pinhole eyes of giant clams (Tridacna maxima).

Giant clams (Tridacna spp.) have several hundred small pinhole-type eyes on the exposed mantle. They respond by withdrawing the mantle to movements of dark objects, even if these cast no shadow on the animal as a whole. I investigated this 'sight reaction' using black and white square-wave gratings whose phase abruptly changed so that the white areas became dark and vice versa. Gratings with periods of 13.5 degrees were ineffective, but gratings of 20.7 degrees caused partial retraction of mantles or siphons. This implies an acceptance angle for the best-resolving eyes of between 8.7 degrees and 21.8 degrees. A single black spot was effective if its angular diameter was 13.5 degrees but not 11.7 degrees. The mean threshold for the pure dimming of a large field was a decrease of 12.3%, but responses increased in strength up to a dimming of 35%. Anatomically the eyes are ca. 400 microm deep from aperture to receptors, the aperture has a mean diameter of 90 microm and the receptors are 25 microm across. This gives an angular acceptance angle for single receptors of 16.5 degrees, which is completely consistent with the behavioural measurements.

Animals↗
PubMed2002

The organization of visually mediated actions in a subject without eye movements.

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.

Activities of Daily Living↗