102,059 research outputs found
Gestalt's principles in the brain: left frontal eye field and the rule of good continuation
No full textAttention has memory: Priming for the size of attentional focus.
No full textRepeating the same target's features or spatial position, as well as repeating the same context (e.g. distractor sets) in visual search leads to a decrease of reaction times. This modulation can occur on a trial by trial basis (the previous trial primes the following one), but can also occur across multiple trials (i.e. performance in the current trial can benefit from features, position or context seen several trials earlier), and includes inhibition of different features, position or contexts besides facilitation of the same ones. Here we asked whether a similar implicit memory mechanism exists for the size of the attentional focus. By manipulating the size of the attentional focus with the repetition of search arrays with the same vs. different size, we found both facilitation for the same array size and inhibition for a different array size, as well as a progressive improvement in performance with increasing the number of repetition of search arrays with the same size. These results show that implicit memory for the size of the attentional focus can guide visual search even in the absence of feature or position priming, or distractor's contextual effects
Modulation of cortical oscillatory activities induced by varying single-pulsetranscranial magnetic stimulation intensity over the left primary motor area: a combined EEG and TMS study.
No full textCombined transcranial magnetic stimulation/electroencephalography (TMS/EEG) was used to study the activation and interaction of cortical regions to a variety of focused sub- and suprathreshold magnetic pulses over the left primary motor cortex (M1) in ten healthy subjects. Five single-pulse TMS conditions were performed based on the individual resting motor threshold (RMT): (1) 80%; (2) 100%; (3) 120%; (4) 130%; and (5) sham. Simple self-paced movements of the right first finger were also executed. We evaluated the reactions to magnetic stimulation and movement conditions using event-related power and event-related coherence transformations of alpha and beta rhythms. Event-related power reflected regional oscillatory activity of neural assemblies, while event-related coherence reflected the inter-regional functional coupling of oscillatory neural activity. The event-related power transformation revealed that the magnetic pulse modulated cortical oscillations within the first half second for both frequency ranges. For the alpha rhythm, threshold TMS induced a small decrease in the amplitude of EEG oscillations over the stimulation site, while for both rhythms, a progressive synchronization was observed as the intensity of TMS was increased in both hemispheres. Movement onset produced a greater bilateral decrease of power compared with the effects of a magnetic pulse. The event-related coherence revealed that TMS enhanced the electrode connectivity of both hemispheres. Additionally, it was more enhanced within the first 500 ms following stimulation and was seen only for the alpha frequency rhythm. The increase of functional connectivity between cortical areas was minor for magnetic stimulation conditions compared with that for finger movements. The single-pulse TMS over M1 partially modulated the motor cortex generators of oscillatory activity, while a simple active self-paced movement of the right first finger induced greater cortex activation and coupling between cortical regions. We propose that finger movements impose higher functional demands on the motor system compared to artificial magnetic stimulation. These findings are consistent with the possibility that the human motor system may be based on network-like oscillatory cortical activity and might be modulated by brief electromagnetic sub- and suprathreshold pulses applied to M1, suggesting a phenomenon of resetting
Changes of motor cortical excitability in human subjects from wakefulness to early stages of sleep: a combined transcranial magnetic stimulation and electroencephalographic study.
No full textThe effect of sleep on human motor cortical excitability was investigated by evaluating the latency and amplitude of motor evoked potentials in ten subjects using transcranial magnetic stimulation. Motor evoked potentials and electroencephalographic data were recorded simultaneously and analyzed. Recordings were performed before, during and after a sleep period. A significant decrease in motor evoked potentials amplitude and a slight change in motor evoked potentials latency were noted in the recordings during the different sleep stages with a return to baseline values on awakening. A decrease in motor cortical excitability is suggested as explaining the effect of sleep
Capacità Innovativa a Rischio
No full textArticolo sui problemi e le sfide dell'innovazione nel nostro paese
The principle of good continuation in space and time can guide visual search in the absence of priming and contextual cues
No full textPrevious research has shown that repetition of the same target features and/or spatial location over time can improve detection, discrimination, and identification. It has also been shown that repetition of the same distractor features or spatial layout can similarly improve search performance. Thus, it appears that target and distractor features and positions are stored in memory and used to guide visual processes such as object recognition and search. Here we introduce a new paradigm for manipulating the sequential structure of target position across trials independently of target features, position priming, and contextual configuration. Results show that facilitation or inhibition in visual search occurs when the target appears at an implicitly expected or unexpected location, respectively, according to the Gestalt's principle of good continuation of the target's successive positions across trials. These findings provide evidence that the simple rule of good continuation can act as a spatiotemporal cue and guide where to attend while searching for the target
Experience enhances texture saliency by reducing behavioural and cortical responses to irrelevant texture features
No full text
Specificities of learning in combined-feature search: implications for underlying coding mechanisms
No full textEleven subjects were trained with 1200 trials of search for a 180°-rotated letter L amongst 90°-counterclockwise-rotated Ls, then tested with three transfer stimuli in which target, distractors, or both were changed. According to signal detection theory, learning both increases signal enhancement and external noise exclusion by enlarging the distance between target and distractor response distributions (Dosher and Lu, 1998 Proceedings of the National Academy of the USA 95 13988 - 13993). Similarly, the SERR (search via recursive rejection ) model (Humphreys and Muller, 1993 Cognitive Psychology 25 43 - 110) would assume a learning process based upon boosting of target template and distractor grouping and rejection. Finally, the FRS (Fogel, Rubenstein, and Sagi) model of texture segmentation [Sagi, 1991, in Channels in the Visual Nervous System: Neurophysiology, Psychophysics and Models Ed. B Blum (London and Tel Aviv: Freund) pp 397 - 424] would assume a learning process based on the tuning of the appropriate filters to the orientation of target and/or distractor elements at the spatial frequency corresponding to the size of whole elements. Our results show that learning transfers to a stimulus where low-pass-filtered orientation of the target and distractor is the same (changing either target or distractors); learning does not transfer to a stimulus where both target and distractors are changed; learning abolishes the differences between present and absent responses. Learning may be based upon either additive internal noise reduction and external noise exclusion (Dosher and Lu, 1998), or target template enhancement and distractor grouping and rejection (Humphreys and Muller, 1993)
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