Visual threshold changes resulting from spontaneous saccadic eye movements.

Persisting asymmetries in the motility and posture of preterm infants after term age is a common finding, but their diagnostic and prognostic significance has proved to be difficult to interpret. It has been claimed that if an asymmetry is of central origin, then it should be most prominently detectable in infantile reactions that persist beyond the age when they should have disappeared. We hypothesis that motor asymmetries in preterm infants without a major risk for neurological problems may stem from a high degree of active muscle power in the trunk that continues to be present after 12 weeks corrected age. In order to test this hypothesis, 34 preterm infants with a low risk for neurological complications were compared to a group of 17 fullterm infants at 18 weeks of (corrected) age for the presence or absence of motor asymmetries. None of the full-term infants showed asymmetrical motor behaviour, while within the preterm group a significant number did, in particular those who were small for gestational age. A significant relationship between motor asymmetries and a high degree of muscle power in the trunk at this age was found in the preterm group. Asymmetrical active muscle power at 18 weeks had a good predictive value for asymmetrical locomotor, hand and eye functions at 52 weeks.

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PubMed1997

The scintillating grid illusion.

Disk-shaped luminance increments were added to the intersections of a Hermann grid consisting of medium grey bars on a black background. Illusory spots, darker than the background, were perceived as flashing within the white disks with each flick of the eye. This striking phenomenon may be referred to as the scintillating grid illusion. We determined the conditions necessary for cancelling the Hermann grid illusion, as well as the luminance requirements and the size ratio between disks and bars that elicits the scintillation effect. The fact that scanning eye movements are necessary to produce the scintillation effect sets it apart from the Hermann grid illusion.

Eye Movements↗

PubMed1997

Motor and perceptual responses to horizontal and vertical eye vibration in humans.

Previous studies have shown that low amplitude/high frequency mechanical vibration applied to the human eye muscles results in the illusory movement of a luminous spot fixated in total darkness. The aim of the present study was to investigate whether a vibration-induced motor response also occurs in eye muscles, and to check whether the visual illusions actually result from the proprioceptors being activated by the vibration, or whether they are simply due to the retinal slip induced by the reflex eye movement. The effects of the vibratory stimuli on the inferior rectus (IR) and lateral rectus (LR) muscles were evaluated by recording subjects' eye position changes. When applied to the IR muscle, vibration effectively elicited an upward visual illusion accompanied by a small downward ocular rotation, whereas when applied to the LR muscle, it also induced horizontal visual illusion, which was less frequent and weaker than the vertical one, but no ocular rotation. We concluded that visual illusions of this kind cannot be attributable to the retinal motion of the image of the fixated point. The difference between the vertical and horizontal vibratory motor responses is discussed as regards the particular role that oculo-muscular proprioception may play in the vertical muscles.

Eye Movements↗