Perceptual experiences may arise from neuronal activity patterns in mammalian neocortex. We probed mouse neocortex during visual discrimination using a red-shifted channelrhodopsin (ChRmine, ...discovered through structure-guided genome mining) alongside multiplexed multiphoton-holography (MultiSLM), achieving control of individually specified neurons spanning large cortical volumes with millisecond precision. Stimulating a critical number of stimulus-orientation-selective neurons drove widespread recruitment of functionally related neurons, a process enhanced by (but not requiring) orientation-discrimination task learning. Optogenetic targeting of orientation-selective ensembles elicited correct behavioral discrimination. Cortical layer-specific dynamics were apparent, as emergent neuronal activity asymmetrically propagated from layer 2/3 to layer 5, and smaller layer 5 ensembles were as effective as larger layer 2/3 ensembles in eliciting orientation discrimination behavior. Population dynamics emerging after optogenetic stimulation both correctly predicted behavior and resembled natural internal representations of visual stimuli at cellular resolution over volumes of cortex.
Classic Gestalt examples of perceptual grouping entail arrays of disconnected surfaces that are grouped on the basis of the surfaces' relative similarity or proximity. However, most natural ...environments contain multiple objects, each with multiple, connected surfaces. Moreover, an object in a scene is likely to partially occlude other objects in the 2-dimensional retinal projection of the scene. A central question, therefore, is how the visual system forms a 3-dimensional representation of multi-object scenes by determining which surfaces belong to which objects. To this end, a recently developed dynamic grouping methodology determines whether pairs of surfaces are grouped together on the basis of the direction in which motion is perceived across a surface when its luminance is perturbed. It is shown using this method that the visible surfaces of a partially occluded object are perceptually grouped when they are plausibly connected and represented in a depth plane behind the occluding object. Invisible connectivity (amodal completion) as well as connectivity established by a visible surface have a powerful influence on the grouping of surfaces. However, for neither kind of connectivity is grouping affected by the distance between the surfaces. This absence of a distance/proximity effect on grouping is obtained when the space between to-be-grouped surfaces is filled with other surfaces. It contrasts with the strong effect of distance/proximity on the grouping of disconnected surfaces, and on the clarity of illusory contours formed between disconnected contours. It is concluded that distance/proximity is an operative grouping variable only when there is empty space between the to-be-grouped surfaces.
El presente estudio analiza hasta qué punto las representaciones de cantidad asociadas a los números arábigos (e.g., 7) influyen en su propio reconocimiento. La existencia de respuestas más rápidas ...cuanto mayor es la distancia numérica entre pares de dígitos en tareas perceptivas (e.g., ¿son iguales 5 y 9?; ¿es 9 un 5?) ha sido la principal evidencia a favor de la automaticidad del acceso a las representaciones de cantidad y, por tanto, de la influencia de procesos top-down sobre el reconocimiento de dígitos. Sin embargo, estudios recientes han demostrado que cuando se incluye como predictor la similitud perceptiva entre los dígitos, el efecto de distancia deja de ser predictor válido en tareas que analizan procesos visuales tempranos como la codificación e identificación, siendo la distancia relevante sólo cuando la tarea es más tardía y demanda conocimiento cuantitativo (e.g., ¿qué número es mayor/menor entre 5 y 9?). Añadiendo una nueva variable a la cuestión, la carga de procesamiento, se ha encontrado que las representaciones de cantidad intervienen en la etapa de identificación, pero sólo cuando aparecen múltiples estímulos. La presente investigación plantea si aumentar la carga de procesamiento en la fase más temprana del proceso perceptivo, la codificación, concederá también un papel a la distancia numérica. Veinte participantes debían decidir si dos dígitos presentados simultáneamente eran iguales o diferentes bajo dos condiciones, una con carga perceptiva (dígitos flanqueados por símbolos) y otra sin carga (sólo los dígitos). Los resultados muestran que en ambas condiciones el factor predictivo era la similitud perceptiva. La carga de procesamiento perceptivo, a pesar de aumentar los tiempos globales de respuesta, no modificó el valor de los predictores. Palabras clave: cognición numérica; procesamiento numérico; reconocimiento visual; percepción; semántica; procesos de codificación. The present study examines the extent to which quantity representations associated with Arabic numerals (e.g., 7) influence how these numbers are recognised. The existence of faster responses in perceptual tasks (e.g., are 5 and 9 the same? is the following stimuli the number 5?) when the numerical distance between digit pairs is greater has thus far been the main evidence in favour of the automaticity of access to quantity representations and, therefore, of the influence of top-down processes on digit recognition. However, recent studies have shown that when perceptual similarity between digits is included as a predictor, the distance effect ceases to be a valid predictor in tasks that analyse early visual processes such as encoding and identification, with distance being relevant only when the task is later and requires quantitative knowledge (e.g., which number is larger/smaller between 5 and 9?). By adding a new variable to the question, that of processing load, it has been found that quantity representations intervene in the identification stage but only when multiple stimuli appear. The present study asks whether increasing the processing load at the earliest stage of the perceptual process, encoding, also grants a role to numerical distance. Twenty participants were asked to decide whether two simultaneously presented digits were the same or different, this under two conditions: in the load condition digits were flanked by symbols, in the no-load condition only the two single- digits were presented. Results were similar in both load conditions: perceptual similarity was the only valid predictor. Although perceptual load caused an increase in overall response times, it did not modify the predictive value of similarity and numerical distance. Keywords: numerical cognition; numerical processing; visual recognition; perception; semantics; encoding processes.
In the vertebrate brain, sensory experience plays a crucial role in shaping thalamocortical connections for visual processing. However, it is still not clear how visual experience influences tissue ...homeostasis and neurogenesis in the developing thalamus. Here, we reported that the majority of SOX2-positive cells in the thalamus are differentiated neurons that receive visual inputs as early as stage 47 Xenopus. Visual deprivation (VD) for 2 days shifts the neurogenic balance toward proliferation at the expense of differentiation, which is accompanied by a reduction in nuclear-accumulated β-catenin in SOX2-positive neurons. The knockdown of β-catenin decreases the expression of SOX2 and increases the number of progenitor cells. Coimmunoprecipitation studies reveal the evolutionary conservation of strong interactions between β-catenin and SOX2. These findings indicate that β-catenin interacts with SOX2 to maintain homeostatic neurogenesis during thalamus development.
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