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Spatial Representation
Eye/Hand Coordination



My PhD consisted of three main themes; spatial representation, attention disengagement and eye-hand coordination.

Spatial representation

As gaze shifts from object to object, the retinal co-ordinates of environmental features change. A robust spatial perception requires the combination of retinal and extra-retinal information to produce a body-centred representation (Abrams, 1992).

The double-step saccade paradigm (DSSP) involves consecutive eye movements to sequentially flashed targets. On the standard version of the task, both targets disappear prior to initiation of the first saccade, creating a spatial dissonance between retinocentric information of the second target and the movement needed to reach it (Heide, Blankenburg, Zimmermann, Kompf, 1995).

 During development of the visual system an infant will correctly respond to the double-step saccade paradigm by about seven months of age (Gilmore and Johnson, 1997).

I carried out three versions of the DSSP. The traditional version with a target duration of 100ms, an middle version with a target duration of 250ms and an easy version with a target duration of 500ms.


Attention disengagement

 Posnerís model of covert attention states that a covert shift of attention involves disengaging from the fixation point, shifting attention to a new target and re-engaging on the new target.  These three processes must occur before an eye movement can be initiated (Posner, 1984).

The gap paradigm: A temporal gap inserted between fixation offset and target onset shortens time taken to initiate a saccade (Saslow, 1967). This has since been called the gap effect, and consists of two conditions; the gap condition, when a temporal gap is inserted between target onset and target offset, and the overlap condition, when target onset and target offset overlap. Shorter saccade latencies are found in the gap condition and the difference between saccade latencies on gap and overlap trials indicates the time taken to disengage attention.

Eye-Hand Coordination

Visual feedback is vital for fast and accurate hand movements, and as such an efficient co-ordination of the eye and hand is needed. The way the eye and hand are co-ordinated has been under scrutiny for many years.

Double-step pointing paradigm: Research using a target jump paradigm (location of the target shifts during the eye movement) has shown that if the target jump occurred early enough, then a smooth hand movement was made to the new target location with participants unaware of the move (Goodale, Pelission, & Prablanc, 1986). These findings suggest that when rapid eye and hand movements are directed to a target, a set of initial signals are sent to the muscles controlling the eye and hand. These signals contain information regarding the position of the target on the retina. Following the first saccade to the target these signals are updated using the extra-retinal information gained during the eye movement.