Daniela Zambarbieri

Saccade latency toward auditory targets depends on the relative position of the sound source with respect to the eyes

The latency of saccadic eye movements evoked by the presentation of auditory and visual targets was studied while starting eye position was either 0 or 20 deg right, or 20 deg left. The results show that for any starting position the latency of visually elicited saccades increases with target eccentricity with respect to the eyes. For auditory elicited saccades and for any starting position the latency decreases with target eccentricity with respect to the eyes. Therefore auditory latency depends on a retinotopic motor error, as in the case of visual target presentation.

Eye movement analysis of reading from computer displays, eReaders and printed books

Citation information: Zambarbieri D & Carniglia E. Eye movement analysis of reading from computer displays, eReaders and printed books. Ophthalmic Physiol Opt 2012, 32, 390–396.. doi: 10.1111/j.1475‐1313.2012.00930.x

EYE-HEAD COORDINATION TOWARD AUDITORY AND VISUAL TARGETS IN HUMANS

Eye-head coordination during gaze orientation toward auditory targets in total darkness has been examined in human subjects. The findings have been compared, for the same subjects, with those obtained by using visual targets. The use of auditory targets when investigating eye-head coordination has some advantages with respect to the more common use of visual targets: (i) more eccentric target positions can be presented to the subject; (ii) visual feedback is excluded during the execution of gaze displacement; (iii) complex patterns of saccadic responses can be elicited. This last aspect is particularly interesting for examining the coupling between the eyes and the head displacements. The experimental findings indicate that during gaze orientation toward a visual or an auditory target the central nervous system adopts the same strategy of using both the saccadic mechanism and the head motor plant. In spite of a common strategy, qualitative and quantitative parameters of the resulting eye-head coordination are slightly different, depending on the nature of the target. The findings relating to patterns of eye-head coordination seem to indicate a dissociation between the eyes and the head, which receive different motor commands independently generated from the gaze error signal. The experimental findings reported in this paper have been summarized in a model of the gaze control system that makes use of a gaze feedback hypothesis through the central reconstruction of the eye and head positions.

The latency of saccades toward auditory targets in humans.

Auditory targets can be used to evoke saccadic eye movements since they provide a position reference signal in space. Comparison of the characteristics of saccades evoked by both visual and auditory stimuli can give further information on the oculomotor control system. In particular, the latency of auditory saccades evoked in different experimental situations, such as the step, gap and overlap protocols, and with different starting positions of the eyes in the orbit can provide useful insight into the central processing underlying saccade generation. The aim of this chapter is to provide a review of auditory saccade characteristics and to present latency data obtained in human subjects in different experimental conditions.

NIRS monitoring of muscle contraction to control a prosthetic device

The fitting of upper-extremity amputees requires special efforts, and its significance has been increased by the development of the myoelectrically controlled prosthetic arm. This solution is not free of problems due to the nature of the amputation, to the electromagnetic noise affecting the myelectrical signal and to the perspiration due to the contact between socket and the residual limb. Starting from the fact that NIRS and electromyographic signals are similar during a muscle contraction, we have first studied the NIRS signal during forearm muscle contractions in normal and amputee subjects. Then a new system to interface the NIRS unit and the myoelectrical prosthetic hand has been developed. The NIRS unit has been used as optical sensor and all the operations (I/O and signal processing) are performed via software. This system has been tested on normal and amputee subjects performing hand grasping using a visual biofeedback control scheme. All the subjects have been able to perform these operations demonstrating the NIRS technique. This could represent an alternative solution for controlling a prosthetic device.

Quantitative evaluation of saccadic eye movements

Saccadic eye movement analysis is becoming increasingly quantitative; thus, an appropriate statistical methodology is needed both for normative data and for single subject evaluation. By assessing normative data in 76 healthy subjects, the authors demonstrated that the amplitude/duration (A/D) and amplitude/peak velocity (A/Vp) relationships, as well as latency, are age-dependent. They did not find a relationship between precision and, respectively, age and target offset. Accordingly, they propose that single subject evaluation should be based on A/D and A/Vp relationships in their entirety, with both the mean and distribution of individual values as the basis for precision and latency.

A Stochastic Model of Central Processing in the Generation of Fixation Saccades

Fixation saccades evoked by the presentation of external targets are the results of three distinct processes: acquisition of sensory information, central reconstruction of target position, and execution of eye movement. Most of the models of the saccadic system presented in the literature (Young, 1962; Young et al., 1968; Robinson, 1973, 1975; Jurgens et al., 1981) were mainly concerned with the execution process. They were basically aimed to the interpretation of the amplitude-duration and amplitude-peak velocity characteristics of saccades elicited by the presentation of visual targets. An appropriate reference signal was assumed to be available at the execution level. Depending on whether a retinotopic or a craniotopic (spatial) saccade organization was assumed, the reference signal was target position relative to the eyes or target position relative to the head.

A clinically oriented approach to smooth pursuit eye movement quantitative evaluation

The electrooculographic technique was used to record smooth pursuit eye movements in 71 healthy subjects homogeneously distributed within an age range between the 2nd and the 6th decades. The target moved at constant velocity (triangular ramps) and 9 different target velocities (V), from 10 deg/s to 50 deg/s were considered and presented according to pseudorandom sequence. Ad hoc software suppressed catch‐up saccades so that a pursuit index (PI) value was computed for each ramp taking into account only the smooth pursuit tracking modality. It was demonstrated that the relationship between V and PI could be described by the linear model PI =a + b* V. Pursuit index was proved to be influenced by the age of subject (decade factor in the analysis of variance), since an almost linear increase in b values yields a reduction of pursuit index values. The method was tested in 22 multiple sclerosis patients and an association was found between the occurrence of cerebellar signs and the reduction of a value.

The generation of vestibular nystagmus: a neural network approach

This study investigates how the saccadic components (quick phases) of vestibular nystagmus are generated. We propose a neural network model for the vestibule saccadic pathway, which shows dynamic adaptation of the quick phase parameters in order to faithfully reproduce the vestibular nystagmus. A structure similar to that proposed in this paper is likely to exist in the neural pathway linking the vestibular nuclei to the PPRF (paramedian pontine reticular formation) through the nucleus prepositus hypoglossi.

Learning processes in the vestibulo-saccadic pathway

This study investigates the way in which the saccadic components (quick phases) of vestibular nystagmus are generated. We propose a neural network model for the vestibule saccadic pathway, which shows dynamic adaptation of the quick phase parameters in order to faithfully reproduce the vestibular nystagmus.