Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

The journal of neuroscience : the official journal of the Society for Neuroscience.

The computational brain: Patricia S. Churchland and Terrence J. Sejnowski (MIT Press, Cambridge, MA, 1992); xi, 544 pages, $39.95

Atlas of the Human Brain.

This study addresses the role of cognitive control in the initiation and execution of familiar and unfamiliar movement sequences. To become familiar with two movement sequences participants first practiced two discrete key press sequences by responding to two fixed series of 6-key specific stimuli. In the ensuing test phase they executed these two familiar and also two unfamiliar keying sequences while there was a two-third chance a tone was presented together with one randomly selected key specific stimulus in each sequence. In the counting condition of the test phase participants counted the low pitched (i.e., target) tones. By and large the results support the dual processor model in which the prime role of the cognitive processor shifts from executing to initiating sequences while the gradual development of motor chunks allows a motor processor to execute the sequences. Yet, the results extend this simple model by suggesting that with little practice sequence execution is based also on some non-cognitive (perhaps associative) learning mechanism and, for some participants, on the use of explicit sequence knowledge. Also, after extensive practice the cognitive processor appears to still contribute to slower responses. The occurrence of long interkey intervals was replicated suggesting that fixed 6-key sequences include several motor chunks. Yet, no indication was found that the cognitive processor is responsible for concatenating these chunks.

/pdf/cognitive-processing-in-new-and-practiced-discrete-keying-2ozc3yb24n.pdf

Cognitive processing in new and practiced discrete keying sequences

quickpsy is a package to parametrically fit psychometric functions. In comparison with previous R packages, quickpsy was build to easily fit and plot data for multiple groups. Here, we describe the standard parametric model used to fit psychometric functions and the standard estimation of its parameters using maximum likelihood. We also provide examples of usage of quickpsy, including how allowing the lapse rate to vary can sometimes eliminate the bias in parameter estimation, but not in general. Finally, we describe some implementation details, such as how to avoid the problems associated to round-off errors in the maximisation of the likelihood or the use of closures and non-standard evaluation functions.

/pdf/quickpsy-an-r-package-to-fit-psychometric-functions-for-3a0eyw6zgl.pdf

quickpsy: An R Package to Fit Psychometric Functions for Multiple Groups

When a ﬂash is presented in spatial alignment with a moving stimulus, the ﬂash appears to lag behind (the ﬂash-lag effect).The motion of the object can inﬂuence the position of the ﬂash, but there may also be a reciprocal effect of the ﬂash on themoving object. Here, we demonstrate that this is the case. We show that when a ﬂash is presented near the moving object,the ﬂash-lag effect does not depend greatly on the duration of the preﬂash trajectory. However, when the ﬂash is presentedsufﬁciently far from the moving object, the ﬂash-lag effect increases with the duration of the preﬂash trajectory, until itreaches an asymptotic level. We also show that the interaction of the near ﬂash can occur when it is task irrelevant. Finally,using the motion aftereffect, we demonstrate that motion signals are involved in the time evolution of the ﬂash-lag effect.Keywords: ﬂash-lag effect, temporal mechanisms, spatial mechanisms, motion aftereffectCitation: Linares, D., Lopez-Moliner, J., & Johnston, A. (2007). Motion signal and the perceived positions of moving objects.Journal of Vision, 7(7):1, 1

/pdf/motion-signal-and-the-perceived-positions-of-moving-objects-cldpf99ub3.pdf

Motion signal and the perceived positions of moving objects.

We easily adapt to changes in the environment that involve cross-sensory discrepancies (e.g., between vision and proprioception). Adaptation can lead to changes in motor commands so that the experienced sensory consequences are appropriate for the new environment (e.g., we program a movement differently while wearing prisms that shift our visual space). In addition to these motor changes, perceptual judgments of space can also be altered (e.g., how far can I reach with my arm?). However, in previous studies that assessed perceptual judgments of space after visuomotor adaptation, the manipulation was always a planar spatial shift, whereas changes in body perception could not directly be assessed. In this study, we investigated the effects of velocity-dependent (spatiotemporal) and spatial scaling distortions of arm movements on space and body perception, taking advantage of immersive virtual reality. Exploiting the perceptual illusion of embodiment in an entire virtual body, we endowed subjects with new spatiotemporal or spatial 3D mappings between motor commands and their sensory consequences. The results imply that spatiotemporal manipulation of 2 and 4 times faster can significantly change participants’ proprioceptive judgments of a virtual object’s size without affecting the perceived body ownership, although it did affect the agency of the movements. Equivalent spatial manipulations of 11 and 22 degrees of angular offset also had a significant effect on the perceived virtual object’s size; however, the mismatched information did not affect either the sense of body ownership or agency. We conclude that adaptation to spatial and spatiotemporal distortion can similarly change our perception of space, although spatiotemporal distortions can more easily be detected.

/pdf/the-effects-of-visuomotor-calibration-to-the-perceived-space-4bmgln4eoi.pdf

The Effects of Visuomotor Calibration to the Perceived Space and Body, through Embodiment in Immersive Virtual Reality

The authors argue that human sequential learning is often but not always characterized by a shift from stimulus- to plan-based action control. To diagnose this shift, they manipulated the frequency of 1st-order transitions in a repeated manual left-right sequence, assuming that performance is sensitive to frequency-induced biases under stimulus- but not plan-based control. Indeed, frequency biases tended to disappear with practice, but only for explicit learners. This tendency was facilitated by visual-verbal target stimuli, response-contingent sounds, and intentional instructions and hampered by auditory (but not visual) noise. Findings are interpreted within an event-coding model of action control, which holds that plans for sequences of discrete actions are coded phonetically, integrating order and relative timing. The model distinguishes between plan acquisition, linked to explicit knowledge, and plan execution, linked to the action control mode.

/pdf/modes-of-executive-control-in-sequence-learning-from-2kgedokmyi.pdf

Modes of Executive Control in Sequence Learning: From Stimulus-Based to Plan-Based Control.

Fast interceptive actions, such as catching a ball, rely upon accurate and precise information from vision. Recent models rely on flexible combinations of visual angle and its rate of expansion of which the tau parameter is a specific case. When an object approaches an observer, however, its trajectory may introduce bias into tau-like parameters that render these computations unacceptable as the sole source of information for actions. Here we show that observer knowledge of object size influences their action timing, and known size combined with image expansion simplifies the computations required to make interceptive actions and provides a route for experience to influence interceptive action.

/pdf/interceptive-timing-prior-knowledge-matters-1yti3vtffo.pdf

Joan López-Moliner

Papers

quickpsy: An R Package to Fit Psychometric Functions for Multiple Groups

Motion signal and the perceived positions of moving objects.

The Effects of Visuomotor Calibration to the Perceived Space and Body, through Embodiment in Immersive Virtual Reality

Modes of Executive Control in Sequence Learning: From Stimulus-Based to Plan-Based Control.

Interceptive timing: prior knowledge matters.