Eye movements in reading and information processing.

Although subjects failed to detect a target displacement if it occurred near the time of a saccadic eye movement (a cognitive visual task), they were still able to point to the center of the target with an unseen pointer (a motor visual task). Pointing performance was not affected by detecting or failing to detect a stimulus displacement. The experiments demonstrate that some information that is available to a motor-oriented visual system is unavailable to the cognitive visual system, under conditions simulating normal perception. Language: en

Relation between cognitive and motor-oriented systems of visual position perception.

Targets were displaced to cancel an apparent displacement induced by a step motion of a background or were held stationary while appearing to jump in an induced displacement. Target and background were then extinguished, and the subject pointed to the target’s last position. When the target had appeared to move but did not, background position did not significantly affect pointing; when the target had moved but appeared to remain stationary (displacement canceled by opposite induced displacement), pointing depended upon the target’s egocentric position. A similar result was obtained with sinusoidal motion. In terms of a two visual-systems hypothesis, the motor system uses more veridical spatial information and is less affected by relative changes in two retinal signals than is the cognitive system.

/pdf/segregation-of-cognitive-and-motor-aspects-of-visual-4ulnt7ymac.pdf

Segregation of cognitive and motor aspects of visual function using induced motion

To control force accurately under a wide range of behavioral conditions, the central nervous system would either require a detailed, continuously updated representation of the state of each muscle (and the load against which each is acting) or else force feedback with sufficient gain to cope with variations in the properties of the muscles and loads. The evidence for force feedback with adequate gain or for an appropriate central representation is not sufficient to conclude that force is the major controlled variable in normal limb movements.Morton's hypothesis, that length is controlled by a follow-up servo, has a number of difficulties related to the delays, gains, variability, and specificity in feedback pathways comprising potential servo loops. However, experimental evidence is consistent with these pathways providing servo assistance for some movements produced by coactivation of α- and static γ-motoneurons. Dynamic γ-motoneurons may provide an additional input for adaptive control of different types of movements.The idea that feedback is used to compensate for changes in muscle stiffness has received experimental support under static postural conditions. However, reflexes tend to increase rather than decrease the range of variation in muscle stiffness during some cyclic movements. Theoretical problems associated with the regulation of stiffness are also discussed. The possibilities of separate control systems for velocity or viscosity are considered, but the evidence is either negative or lacking. I conclude that different physical variables can be controlled depending on the type of limb movement required. The concept of stiffness regulation is also useful under some conditions, but should probably be extended to the regulation of the visco-elastic properties (i.e., the mechanical impedance) of a muscle or joint.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00013327

What muscle variable(s) does the nervous system control in limb movements

As people examine their world, the proximal stimulus changes position on their retinae with every saccade, but they perceive the world as being stable. This phenomenon of visual stability was explored by making changes in natural, full-color pictures during selected saccades as observers examined them in preparation for a recognition test. In Experiment 1, the pictures were displaced up, down, left, or right by 0.3, 0.4, or 1.2 degrees. In Experiment 2, the pictures were expanded or contracted by 10% or 20%. As a secondary task, subjects pressed a button when a change was detected. Three results from previous studies with simpler stimuli did not generalize. Evidence suggests that subjects' detection of image changes primarily involves the use of local information in the region of the eyes' landing position. A saccade target theory of visual stability is proposed.

/pdf/visual-stability-across-saccades-while-viewing-complex-46nf2l4kbb.pdf

Stark Lawrence

Papers

Saccadic suppression of image displacement.