The effect of superior colliculus ablation on saccades elicted by cortical stimulation

Human Activity Recognition (HAR) is a burgeoning field of study due to its real-life applications in the medical field, the e-health system, and elder care or care of physically impaired people in a smart healthcare environment. Using sensors built into wearable devices, such as smartphones, HAR provides an opportunity to identify human behavior and better understand an individual’s health. Improving the classification performance of human activities is an academic and industrial focus. Feature selection can affect classification performance: redundant and irrelevant features increase the learning difficulty of the classification model, cause overfitting, reduce classification performance, decrease interpretability, and reduce generalizability. Many preceding studies showed the defectiveness of feature selection results, which causes difficulties for professionals in a variety of fields (e.g., medical practitioners) to analyze and interpret the obtained feature subsets. Random Forest (RF) based feature selection methods select more interpretable features than other methods. However, RF-based feature selection methods are highly biased. Herein, we propose a novel RF-based feature selection method, namely modified Guided Regularized Random Forest (mGRRF), using permutation importance to overcome this. To prove the effectiveness of the proposed feature selection method, we conduct experiments using a public standard HAR dataset. Five classifiers, such as random forest, k-nearest neighbors, logistic regression, support vector machine, and xgboost, are used to recognize human activities after selecting the relevant and vital features using mGRRF. Experimental results indicate that with mGRRF-based features, the recognition accuracy is generally improved to 98% or 7% better than when all the extracted statistical features are used.

We conduct a comparative evaluation of the visual systems from the retina to the muscles of the mouse and the macaque monkey noting the differences and similarities between these two species. The topics covered include (1) visual-field overlap, (2) visual spatial resolution, (3) V1 cortical point-image [i.e., V1 tissue dedicated to analyzing a unit receptive field], (4) object versus motion encoding, (5) oculomotor range, (6) eye, head, and body movement coordination, and (7) neocortical and cerebellar function. We also discuss blindsight in rodents and primates which provides insights on how the neocortex mediates conscious vision in these species. This review is timely because the field of visuomotor neurophysiology is expanding beyond the macaque monkey to include the mouse; there is therefore a need for a comparative analysis between these two species on how the brain generates visuomotor responses.

The effect of slower responses to validly than invalidly cued targets is known as inhibition of return (IOR). Opposing accounts of IOR have been proposed: one postulates a singular phenomenon explained by oculomotor mechanisms alone, while the other, more diverse account postulates both perceptual-cognitive and motor factors. In our research we considered the relation between motor programming and IOR. In an extended replication of an earlier study, using an eye abduction technique we restricted eye movement in the temporal half-space; this resulted in IOR attenuation in that area, compared to the unrestricted, nasal part of the visual field. Our results contradict the earlier result and demonstrate that IOR does depend on preparation of eye movement, as predicted by the oculomotor priming hypothesis.

Based on two-photon calcium imaging, Histed et al. (2009) concluded that electrical microstimulation of cortical tissue in mammals activates a sparse and distributed population of neurons. This work has been cited by many as proof that electrical microstimulation is nonfocal, which means it may lack the precision needed for applications in neuroprosthetics. We affirm that the generation of stimulation-evoked behaviour is based primarily on the orthodromic conduction of signals originating mainly from the deepest layers of cortex, while the work of Histed et al. is effectively limited to investigating the antidromic activation of lateral projection neurons of the superficial cortex. The apparent sparse activation is a consequence of the pattern of axonal projections based on activating a volume of axons while imaging cell bodies transecting a single plane through the cortex. This creates the false impression that the distribution of activated neurons is sparse and nonfocal. We recommend how two-photon calcium imaging, which is superb for the study of individual and groups of neurons, might be more effectively used to ascertain how electrical stimulation affects the brains of mammals. This is a timely topic since investigators are using electrical microstimulation in animals to develop prosthetic devices to restore sensory and motor functions in disabled patients.

We assess what monkeys see during electrical stimulation of primary visual cortex (area V1) and relate the findings to visual percepts evoked electrically from human V1. Discussed are: (1) the electrical, cytoarchitectonic, and visuo-behavioural factors that affect the ability of monkeys to detect currents in V1; (2) the methods used to ascertain what monkeys see when electrical stimulation is delivered to V1; (3) a corticofugal mechanism for the induction of visual percepts; and (4) the quantity of information transferred to V1 by electrical stimulation. Experiments are proposed that should advance our understanding of how electrical stimulation affects macaque and human V1. This work contributes to the development of a cortical visual prosthesis for the blind. We dedicate this work to the late Robert W. Doty.

Although there is evidence to suggest visual illusions affect perceptual judgments more than actions, many studies have failed to detect task-dependant dissociations. In two experiments we attempt to resolve the contradiction by exploring the time-course of visual illusion effects on both saccadic eye movements and perceptual judgments, using the Judd illusion. The results showed that, regardless of whether a saccadic response or a perceptual judgement was made, the illusory bias was larger when responses were based on less information, that is, when saccadic latencies were short, or display duration was brief. The time-course of the effect was similar for both the saccadic responses and perceptual judgements, suggesting that both modes may be driven by a shared visual representation. Changes in the strength of the illusion over time also highlight the importance of controlling for the latency of different response systems when evaluating possible dissociations between them.