Concurrent processing of saccades

We summarize several experiments indicating that the saccadic system is capable of simultaneously programming two movements toward different goals. This concurrent processing of saccades can lead to the execution of two saccades separated by an extremely short intersaccadic interval. This supports the idea of target competition proposed in Findlay & Walker's article, but suggests a greater degree of parallel processing. We provide evidence that concurrent processing of two saccades is not limited to higher-level planning subsystems; rather, it also involves both regions close enough to the motor output that it can systematically affect saccade trajectory.

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Scheduling and stability aspects of a general class of parallel processing systems

Advances in Applied Probability ◽

10.2307/1427501 ◽

1993 ◽

Vol 25 (1) ◽

pp. 176-202 ◽

Cited By ~ 15

Author(s):

Nicholas Bambos ◽

Jean Walrand

Keyword(s):

Asymptotic Behavior ◽

Parallel Processing ◽

General Class ◽

Processing Time ◽

Arrival Time ◽

System Designer ◽

Scheduling Policy ◽

Concurrent Processing ◽

Random Flow ◽

Random Amount

In this paper we study the following general class of concurrent processing systems. There are several different classes of processors (servers) and many identical processors within each class. There is also a continuous random flow of jobs, arriving for processing at the system. Each job needs to engage concurrently several processors from various classes in order to be processed. After acquiring the needed processors the job begins to be executed. Processing is done non-preemptively, lasts for a random amount of time, and then all the processors are released simultaneously. Each job is specified by its arrival time, its processing time, and the list of processors that it needs to access simultaneously. The random flow (sequence) of jobs has a stationary and ergodic structure. There are several possible policies for scheduling the jobs on the processors for execution; it is up to the system designer to choose the scheduling policy to achieve certain objectives.We focus on the effect that the choice of scheduling policy has on the asymptotic behavior of the system at large times and especially on its stability, under general stationary and ergocic input flows.

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Can parallel processing and competitive inhibition explain the generation of saccades?

Behavioral and Brain Sciences ◽

10.1017/s0140525x99332155 ◽

1999 ◽

Vol 22 (4) ◽

pp. 685-686 ◽

Cited By ~ 4

Author(s):

M. A. Frens ◽

I. T. C. Hooge ◽

H. H. L. M. Goossens

Keyword(s):

Parallel Processing ◽

Competitive Inhibition ◽

Current Knowledge ◽

Saccadic System ◽

Target Article ◽

Winner Take All ◽

Take All

The framework of Findlay & Walker's target article provides a first attempt to model the saccadic system at all levels. Their scheme is based on two main principles. These are “parallel processing of saccade timing and metrics” and “competitive inhibition through winner-take-all strategies.” In our opinion, however, both concepts are in their strictest sense at odds with the current knowledge of the saccadic system, and need to be refined to make the scheme more relevant.

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Superior Colliculus Activity Related to Concurrent Processing of Saccade Goals in a Visual Search Task

Journal of Neurophysiology ◽

10.1152/jn.00501.2001 ◽

2002 ◽

Vol 87 (4) ◽

pp. 1805-1815 ◽

Cited By ~ 102

Author(s):

Robert M. McPeek ◽

Edward L. Keller

Keyword(s):

Superior Colliculus ◽

Rhesus Monkeys ◽

Search Task ◽

Visual Search Task ◽

Saccadic System ◽

Concurrent Processing ◽

Initial Saccade ◽

Preparatory Activity ◽

Winner Take All ◽

Initial Movement

Saccades are typically separated by inter-saccadic fixation intervals (ISFIs) of ≥125 ms. During this time, the saccadic system selects a goal and completes the preparatory processes required prior to executing the subsequent movement. However, in tasks in which competing stimuli are presented, two sequentially executed movements to different goals can be separated by much shorter ISFIs. This suggests that the saccadic system is capable of completing many of the preparatory requirements for a second saccade concurrently with the execution of an initial movement. We recorded single neurons in the superior colliculus (SC) during rapid saccade sequences made by rhesus monkeys performing a search task. We found that during the execution of an initial saccade, activity related to the goal of a quickly following second saccade can be simultaneously maintained in the SC motor map. This activity appears to signal the selection or increased salience of the second saccade goal even before the initial saccade has ended. For movements separated by normal ISFIs (≥125 ms), we did not observe activity related to concurrent processing, presumably because for these longer ISFI responses, the goal of the second saccade is not selected until after the end of the first saccade. These results indicate that, at the time of an initial saccade, the SC does not necessarily act as a strict winner-take-all network. Rather it appears that the salience of a second visual goal can be simultaneously maintained in the SC. This provides evidence that selection or preparatory activity related to the goal of a second saccade can overlap temporally with activity related to an initial saccade and indicates that such concurrent processing is present even in a structure which is fairly close to the motor output.

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Scheduling and stability aspects of a general class of parallel processing systems

Advances in Applied Probability ◽

10.1017/s0001867800025222 ◽

1993 ◽

Vol 25 (01) ◽

pp. 176-202 ◽

Cited By ~ 4

Author(s):

Nicholas Bambos ◽

Jean Walrand

Keyword(s):

Asymptotic Behavior ◽

Parallel Processing ◽

General Class ◽

Processing Time ◽

Arrival Time ◽

System Designer ◽

Scheduling Policy ◽

Concurrent Processing ◽

Random Flow ◽

Random Amount

In this paper we study the following general class of concurrent processing systems. There are several different classes of processors (servers) and many identical processors within each class. There is also a continuous random flow of jobs, arriving for processing at the system. Each job needs to engage concurrently several processors from various classes in order to be processed. After acquiring the needed processors the job begins to be executed. Processing is done non-preemptively, lasts for a random amount of time, and then all the processors are released simultaneously. Each job is specified by its arrival time, its processing time, and the list of processors that it needs to access simultaneously. The random flow (sequence) of jobs has a stationary and ergodic structure. There are several possible policies for scheduling the jobs on the processors for execution; it is up to the system designer to choose the scheduling policy to achieve certain objectives. We focus on the effect that the choice of scheduling policy has on the asymptotic behavior of the system at large times and especially on its stability, under general stationary and ergocic input flows.

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Editorial Special Issue on parallel processing in GIS

International Journal of Geographical Information Systems ◽

10.1080/026937996137783 ◽

1996 ◽

Vol 10 (6) ◽

pp. 667-668 ◽

Cited By ~ 1

Author(s):

R. G. Healey

Keyword(s):

Parallel Processing ◽

Special Issue ◽

Editorial Special Issue

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Behavior in the Brain

Journal of Psychophysiology ◽

10.1027/0269-8803/a000016 ◽

2010 ◽

Vol 24 (2) ◽

pp. 76-82 ◽

Cited By ~ 15

Author(s):

Martin M. Monti ◽

Adrian M. Owen

Keyword(s):

Motor Behavior ◽

Functional Neuroimaging ◽

Brain Activity ◽

Motor Output ◽

The Unconscious ◽

Ethical Implications ◽

Brain Responses ◽

Minimally Conscious ◽

Brain Insults ◽

Brain Behavior

Recent evidence has suggested that functional neuroimaging may play a crucial role in assessing residual cognition and awareness in brain injury survivors. In particular, brain insults that compromise the patient’s ability to produce motor output may render standard clinical testing ineffective. Indeed, if patients were aware but unable to signal so via motor behavior, they would be impossible to distinguish, at the bedside, from vegetative patients. Considering the alarming rate with which minimally conscious patients are misdiagnosed as vegetative, and the severe medical, legal, and ethical implications of such decisions, novel tools are urgently required to complement current clinical-assessment protocols. Functional neuroimaging may be particularly suited to this aim by providing a window on brain function without requiring patients to produce any motor output. Specifically, the possibility of detecting signs of willful behavior by directly observing brain activity (i.e., “brain behavior”), rather than motoric output, allows this approach to reach beyond what is observable at the bedside with standard clinical assessments. In addition, several neuroimaging studies have already highlighted neuroimaging protocols that can distinguish automatic brain responses from willful brain activity, making it possible to employ willful brain activations as an index of awareness. Certainly, neuroimaging in patient populations faces some theoretical and experimental difficulties, but willful, task-dependent, brain activation may be the only way to discriminate the conscious, but immobile, patient from the unconscious one.

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