The double step analysis of rapid manual aiming movements

The present paper examines the control principles underlying rapid manual tracking responses to horizontal double-step stimuli. The paper reports an experiment concerned with responses made to step-stimuli presented in quick succession. The amplitude of the second-step was varied between the initial step-position and the home-base. Double-step response parameters were analysed as a function of the determinant time interval (D) between the second step and the onset of the initial response. The initial response amplitude was observed to vary as a function of D. Amplitude transition functions were constructed representing the transition of the initial response amplitude between the two step positions; their slopes, furthermore, depended on the amplitude of the second target step. No delays in the initial reaction time with the interstimulus interval were observed. Minor delays to the onset of a corrective response were observed. These delays were in part related to a movement time constraint that is independent of any limitations in central processing capacity. The present findings for the manual control system are compared to double-step tracking analyses of the oculomotor control system.     

Response amendments during manual aiming movements to double-step targets

The present paper reports a double-step analysis of a discrete aiming movement. A second target step was presented during the trajectory of the response to an initial step and represented an artificially induced movement error signal. Two stimulus patterns involving steps in the same direction (an undershoot error signal) and opposite direction (an overshoot error signal) to the initial step were examined. Moreover, in a random error condition the subject had no advance information regarding the direction of the error. In a deliberate error condition the subject knew in advance whether any subsequent error would be an undershoot or overshoot. Response parameters were considered as a function of the interstep interval which was randomly varied across trials. In terms of movement time, the standard deviations and a constant amendments score of double-step trials, subjects could respond more appropriately and effectively to a deliberate rather than a random error, and an undershoot error rather than an overshoot error. These results are discussed in terms of a mixed-mode of visuo-spatial error updating and related to the generalized motor program hypothesis.     

Amplitude Scaling Compensates for Serial Delays in Correcting Eye and Arm Movements

Spatial and metrical parameters of the eye and arm movements made by human subjects (N = 7) in response to visual targets that were stepped unexpectedly either once (single step) or twice (double step) were studied. For the double-step, the displacement of a visual target was decreased or increased in amplitude at intervals before and during a movement. Provided the second target step occurred more than 100 ms before the onset of movement, the amplitude of the subjects' first response was altered in the direction of the new target location. But this amplitude scaling was not always sufficient to reach the new target location, and a second corrective response was required. The latency in producing this second response was greatly increased above reaction time latencies of movements to single-step targets, especially when the target change occurred 100 ms or more before movement onset. These findings suggest that even though serial processing limitations delay the production of a second corrective response, continuous parallel processing of visual information enables the amplitude of the first response to be altered with minimal delay. This enables some degree of real-time continuous control by the visuomotor control system.     

Amplitude Scaling Compensates for Serial Delays in Correcting Eye and Arm Movements

Spatial and metrical parameters of the eye and arm movements made by human subjects (N = 7) in response to visual targets that were stepped unexpectedly either once (single step) or twice (double step) were studied. For the double-step, the displacement of a visual target was decreased or increased in amplitude at intervals before and during a movement. Provided the second target step occurred more than 100 ms before the onset of movement, the amplitude of the subjects' first response was altered in the direction of the new target location. But this amplitude scaling was not always sufficient to reach the new target location, and a second corrective response was required. The latency in producing this second response was greatly increased above reaction time latencies of movements to single-step targets, especially when the target change occurred 100 ms or more before movement onset. These findings suggest that even though serial processing limitations delay the production of a second corrective response, continuous parallel processing of visual information enables the amplitude of the first response to be altered with minimal delay. This enables some degree of real-time continuous control by the visuomotor control system.     

Error processing in pointing at randomly feedback-induced double-step stimuli

Two experiments were conducted to determine the spatial and temporal organization of the arm trajectory in human subjects as they pointed to single- and double-step target displacements. Subjects pointed either without (Experiment 1) or with (Experiment 2) vision of their moving hand throughout the trial. In both experiments, target perturbation occurring in double-step trials was clearly perceived by the subjects and was randomly introduced either at the onset or at peak velocity of hand movement. Regardless of whether or not visual reafference from the pointing hand was available, subjects corrected the trajectory of their moving hand to accommodate the double-step. Moreover, asymmetrical velocity profiles were observed for responses to both types of target, with or without vision of the moving hand. The acceleration phase was a fixed pattern independent of the type of step stimulation. However, a clear dissociation, both in the deceleration phase and accuracy of responses to double-step targets, emerged according to the timing of target perturbation. When targets were perturbed at the onset of hand movement, subjects modulated the deceleration phase of their response to compensate for 88 to 100% of the second target displacement. In contrast, when targets were perturbed at peak velocity of hand movement, subjects were unable to modulate the deceleration phase adequately and compensated for only 20 to 40% of the perturbation. These results suggest that motor error is dynamically evaluated during the acceleration phase of a movement toward a perturbed target, allowing amendments to the trajectory to be performed during the deceleration phase. This main corrective process appears to be basically independent of visual reafference from the moving hand.     

A model for the time-order error in contrast discrimination

Trials in a temporal two-interval forced-choice discrimination experiment consist of two sequential intervals presenting stimuli that differ from one another as to magnitude along some continuum. The observer must report in which interval the stimulus had a larger magnitude. The standard difference model from signal detection theory analyses poses that order of presentation should not affect the results of the comparison, something known as the balance condition (J.-C. Falmagne, 1985, in Elements of Psychophysical Theory). But empirical data prove otherwise and consistently reveal what Fechner (1860/1966, in Elements of Psychophysics) called time-order errors, whereby the magnitude of the stimulus presented in one of the intervals is systematically underestimated relative to the other. Here we discuss sensory factors (temporary desensitization) and procedural glitches (short interstimulus or intertrial intervals and response bias) that might explain the time-order error, and we derive a formal model indicating how these factors make observed performance vary with presentation order despite a single underlying mechanism. Experimental results are also presented illustrating the conventional failure of the balance condition and testing the hypothesis that time-order errors result from contamination by the factors included in the model.     

Testing the attention shift hypothesis as an account for the flanker sequence-based congruency modulation in spatial flanker tasks

Smaller Simon effects when stimulus locations are repeated on successive trials rather than alternated have been explained by the attention shift hypothesis, suggesting that shifts of attention result in interfering response codes. We investigated whether the attention shift hypothesis can also explain smaller flanker effects for repeated flankers than for alternated flankers, which occur only with directional information. In 3 peripheral letter identification tasks, target locations were cued by partial or complete flanker stimuli. Experiments 1 and 2 showed that directional flankers elicit shifts of attention. However, Experiment 3 revealed that directional flankers induced inverted cuing effects when reacting to the central target arrow was additionally required. These results are difficult to reconcile with the attention shift hypothesis as an explanation for the congruency reduction with repetitions of directional flankers.     

Dependence of Finger Flexion Force on the Posture of the Nonperforming Fingers During Key Pressing Tasks

In visuomotor tasks that involve accuracy demands, small directional changes in the trajectories have been taken as evidence of feedback-based error corrections. In the present study variability, or intermittency, in visuomanual tracking of sinusoidal targets was investigated. Two lines of analyses were pursued: First, the hypothesis that humans fundamentally act as intermittent servo-controllers was re-examined, probing the question of whether discontinuities in the movement trajectory directly imply intermittent control. Second, an alternative hypothesis was evaluated: that rhythmic tracking movements are generated by entrainment between the oscillations of the target and the actor, such that intermittency expresses the degree of stability. In 2 experiments, participants (N = 6 in each experiment) swung 1 of 2 different hand-held pendulums, tracking a rhythmic target that oscillated at different frequencies with a constant amplitude. In 1 line of analyses, the authors tested the intermittency hypothesis by using the typical kinematic error measures and spectral analysis. In a 2nd line, they examined relative phase and its variability, following analyses of rhythmic interlimb coordination. The results showed that visually guided corrective processes play a role, especially for slow movements. Intermittency, assessed as frequency and power components of the movement trajectory, was found to change as a function of both target frequency and the manipulandum's inertia. Support for entrainment was found in conditions in which task frequency was identical to or higher than the effector's eigenfrequency. The results suggest that it is the symmetry between task and effector that determines which behavioral regime is dominant.     

Cortical dynamics of visual persistence and temporal integration

In a temporal integration experiment, subjects must integrate two visual stimuli, presented at separate times, to perform an identification task. Many researchers have assumed that the persistence of the leading stimulus determines the ability to integrate the leading and trailing stimuli. However, recent studies of temporal integration have challenged that hypothesis by demonstrating that several theories of persistence are incompatible with data on temporal integration. This paper shows that an account of visual persistence given by a neural network model of preattentive vision, called the boundary contour system, explains data on temporal integration. Computer simulations of the model explain why temporal integration becomes more difficult when the display elements are separated by longer interstimulus intervals or are of longer duration or of higher luminance, or are spatially closer together. The model suggests that different mechanisms underlie the inverse duration effects for leading and for trailing elements. The model further predicts interactions of spatial separation, duration, and luminance of the trailing display.     

Stimulus discriminability in the magnitude estimation and category rating of loudness

Thirty-three Ss made category ratings and magnitude estimations of 10 auditory stimuli differing in loudness. The results from each task were examined in terms of the response uncertainty conditional upon each stimulus. The results did not support the suggestion that category judgments are influenced by the relative discriminability of stimuli in a way which is not characteristic of magnitude estimates, but were found to be consistent with the subjective Standard hypothesis. It is argued that the observed quasi-logarithmic relationship between category scale and ratio scale values reflects the constraints placed upon responses in category rating tasks.     

Control of Rapid Arm Movements When Target Position Is Altered During Saccadic Suppression

This experiment examined whether rapid arm movements can be corrected in response to a change in target position that occurs just prior to movement onset, during saccadic suppression of displacement. Because the threshold of retinal input reaches its highest magnitude at that time, displacement of the visual target of a saccade is not perceived. Subjects (N = 6) were instructed to perform very rapid arm movements toward visual targets located 16, 20, and 24 degrees from midline (on average, movement time was 208 ms). On some trials the 20 degrees target was displaced 4 degrees either to the right or to the left during saccadic suppression. For double-step trials, arm movements did not deviate from their original trajectory. Movement endpoints and movement structure (i.e., velocity-and acceleration-time profiles) were similar whether or not target displacements occurred, showing the failure of proprioceptive signals or internal feedback loops to correct the arm trajectory. Following this movement, terminal spatially oriented movements corrected the direction of the initial movement (as compared with the single-step control trials) when the target eccentricity decreased by 4 degrees. Subjects were unaware of these spatial corrections. Therefore, spatial corrections of hand position were driven by the goal level of the task, which was updated by oculomotor corrective responses when a target shift occurred.     

On the role of space and time in auditory processing

Unlike visual and tactile stimuli, auditory signals that allow perception of timbre, pitch and localization are temporal. To process these, the auditory nervous system must either possess specialized neural machinery for analyzing temporal input, or transform the initial responses into patterns that are spatially distributed across its sensory epithelium. The former hypothesis, which postulates the existence of structures that facilitate temporal processing, is most popular. However, I argue that the cochlea transforms sound into spatiotemporal response patterns on the auditory nerve and central auditory stages; and that a unified computational framework exists for central auditory, visual and other sensory processing. Specifically, I explain how four fundamental concepts in visual processing play analogous roles in auditory processing.     

Visually based amendments of aiming movements: a reappraisal of Christina (1970).

The present paper examines the processing of visual information during the initial and corrective phases of an aimed movement. Visual processing in the corrective phase is related to the nature of the error in the initial phase. By producing a deliberate error, the system knows the approximate amplitude and direction in advance, allowing for the preprogramming of the corrective response. The final response, however, awaits visual confirmation with a processing time on the order of 130 msec. This strategy is feasible only if the variability in the initial response is constrained, which is the role of an additional very rapid feedback loop (70 to 100 msec.).     

Shape Integration for Visual Object Recognition and Its Implication in Category-Specific Visual Agnosia

A series of experiments was conducted on a patient (ELM) with bilateral inferior temporal lobe damage and category-specific visual agnosia in order to specify the nature of his functional impairment. In Experiment 1, ELM performed a task of picture/word matching that used line drawings of fruits and vegetables as stimuli. The pattern of confusions exhibited by the patient suggested a failure in processing the full range of shape features necessary for the unique specification of the target relative to other structurally related items. This hypothesis of a shape integration impairment was tested and verified by subsequent visual recognition experiments (Experiments 2-4), which used synthetic stimuli with shapes precisely defined on the dimensions of elongation, curvature, and tapering. Furthermore, it was determined (Experiment 5) that the integration deficit is specific to the retrieval of shape knowledge from memory and does not affect the encoding of the properties of visual stimuli. It is argued that these findings have critical implications for cognitive theories of visual object recognition and for an interpretation of the visual function of the inferior temporal cortex. Finally, it was shown that the patient's deficit for structural knowledge integration is modulated by the semantic properties of the objects (Experiment 6), thereby demonstrating the applicability of the present findings to an explanation of category-specific visual agnosia.     

Concurrent Directional Adaptation of Reactive Saccades and Hand Movements to Target Displacements of Different Size

When eye and hand movements are concurrently aimed at double-step targets that call for equal and opposite changes of response direction (–10° for the eyes, +10° for the hand), adaptive recalibration of both motor systems is strongly attenuated; instead, hand but not eye movements are changed by corrective strategies (V. Grigorova et al., 2013a). The authors introduce a complementary paradigm, where double-step targets call for a –10° change of eye and a ?30° change for hand movements. If compared to control subjects adapting only the eyes or only the hand, adaptive improvements were comparable for the eyes but were twice as large for the hand; in contrast, eye and hand aftereffects were comparable to those in control subjects. The authors concluded that concurrent exposure of eyes and hand to steps of the same direction but different size facilitated hand strategies, but didn't affect recalibration. This finding together with previous one (V. Grigorova et al., 2013a), suggests that concurrent adaptation of eyes and hand reveals different mechanisms of recalibration for step sign and step size, which are shared by reactive saccades and hand movements. However, hand mostly benefits from strategies provoked by the difference in target step sign and size.     

Beyond hypercorrection: remembering corrective feedback for low-confidence errors*

Correcting errors based on corrective feedback is essential to successful learning. Previous studies have found that corrections to high-confidence errors are better remembered than low-confidence errors (the hypercorrection effect). The aim of this study was to investigate whether corrections to low-confidence errors can also be successfully retained in some cases. Participants completed an initial multiple-choice test consisting of control, trick and easy general-knowledge questions, rated their confidence after answering each question, and then received immediate corrective feedback. After a short delay, they were given a cued-recall test consisting of the same questions. In two experiments, we found high-confidence errors to control questions were better corrected on the second test compared to low-confidence errors – the typical hypercorrection effect. However, low-confidence errors to trick questions were just as likely to be corrected as high-confidence errors. Most surprisingly, we found that memory for the feedback and original responses, not confidence or surprise, were significant predictors of error correction. We conclude that for some types of material, there is an effortful process of elaboration and problem solving prior to making low-confidence errors that facilitates memory of corrective feedback.     

Choice reaction times for skilled responses

Two kinds of choice reaction time experiments are reported, both of which make use of a highly overlearned sensori-motor response. When a response is required for each stimulus presented, no increase in reaction time occurs as a function of the number of alternative stimuli available. It is proposed that the increase in choice reaction times commonly thought to accompany an increase in the number of alternative choices provided reflects the unpractised state of the responder. When a response is required for only one out of n possible stimuli, a slight but consistent increase in reaction time takes place with an increase in the number of alternatives. An analogy is drawn between the second experiment and a vigilance task and an expectancy hypothesis is invoked to explain the results.     

Perception of sequentially presented tactile point stimuli

Either two or three brief (10 msec) airjet stimuli were sequentially presented to any of the 24 interjoint regions of the fingers (thumbs excluded). The stimulus onset interval (SOI) ranged from zero (simultaneous presentation) through 200 msec. The S’s task in one part of the experiment was to report the positions stimulated in the order that the stimuli were presented; in a second part it was to rate the apparent motion produced by the stimulus sequence. While the ability of Ss to spatially localize the stimuli was a constant independent of SOI, their ability to temporally order the stimuli depended strongly on SOI. With two stimuli, these sequential errors decayed exponentially with SOI with a time constant of 26 msec. With three stimuli, however, both the sequential errors and equivalent temporal Urnen were more than twice as large as with two stimuli, indicating that the three-stimulus task is considerably more difficult than the two, and that the same simple temporal resolution model does not explain both cases. A model with a constant rate of information uptake, however, can explain both of these cases.     

Central interference in error processing

This study dealt with capacity limitations in error processing. Participants classified digits into three arbitrary categories (initial response). Half were required to correct their errors if an error was detected (correction response), and half were required to produce a second response, regardless of the correctness of the initial response (approval response). Auditory interference was introduced before, during, or after the initial response. Interference stimuli were to be recalled later and were, thus, considered to involve central processes. Results for before showed that although correction responses were elongated, approval responses given after erroneous initial responses were shortened. For during, both correction and approval responses were elongated. On the basis of our findings, we argue that the error process is generated before the erroneous response is given and that it is a central process in terms of being subjected to capacity limitations in the presence of other central processes.     

Illusory conjunctions of forms, objects, and scenes during rapid serial visual search

"Temporal migration" describes a situation in which subjects viewing rapidly presented stimuli (e.g., 9-20 items/s) confidently report a target element as having been presented in the same display as a previous or following stimulus in the sequence. Four experiments tested a short-term buffer model of this phenomenon. Experiments 1 and 4 tested the hypothesis that subjects' errors are due to the demands of the verbal report procedure rather than to perceptual integration. In Experiment 1, 12 color objects were presented at a rate of 9/s. Prior to each sequence, an object was named and subjects responded "yes" or "no" to indicate whether the target element (a black frame) occurred with that object. Consistent with the perceptual hypothesis, the yes/no procedure yielded the same results as the verbal report procedure. Experiment 2 tested the hypothesis that the direction of migration depends on "frame" detection time. Results showed that reaction time to frame detection was significantly faster in trials in which subjects reported the frame on a preceding rather than a following picture. Experiments 3 and 4 used the standard naming procedure and the yes/no procedure to test temporal migration using more complex, interrelated stimuli (objects and scenes). Implications for the use of the temporal migration effect to study visual integration within eye fixations are discussed.