1,721,002 research outputs found
Attention 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
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)
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
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
Corticospinal excitability in human subjects during nonrapid eye movement sleep: single and paired-pulse transcranial magnetic stimulation study
No full textEffects of priming in texture segmentation
No full textThis study aimed at establishing whether, as follows from the perceptual representation system (PRS) hypothesis, mechanisms for coding configural properties in texture segmentation are similar in perception and short-term perceptual memory (STPM). We investigated whether implicit STPM for a texture bar oriented 45° clockwise or counterclockwise produced different priming effects on texture segmentation, depending on whether bar orientation was parallel or orthogonal to its line texture elements. Orientation discrimination in the first block was at threshold (74%) for parallel but not for orthogonal (40%) bars. Training brought all performances to ceiling, suggesting that training makes parallel and orthogonal bars equally salient. However, performance was worse when the stimulus in the nth trial was preceded by a parallel bar rather than an orthogonal one, regardless of whether the bar in the nth trial was parallel or orthogonal; this (priming effect) decreased with training. These results indicate that in the first trials the parallel, more salient, bar is coded in the PRS by low-spatial-frequency mechanisms selective to the whole-bar orientation, and that this STPM may interfere with local texture segmentation. On the other hand, the orthogonal, less salient, bar is coded in the PRS by high-spatial- frequency channels selective for texture elements or texture borders and interferes less with texture processing. Learning equates salience of parallel and orthogonal bars so that the memory code, as well as the sensory processing, become similar for the two kinds of texture. These findings support the view of a common mechanism (namely, PRS) responsible for visual processing and STPM of visual stimuli, which operate at early levels of the visual stream
Perceptual learning modulates electrophysiological and psychophysical response to visual texture segmentation in Humans
No full textWe investigated the mechanisms that allow, via perceptual learning, selective modulation of a visual line-texture figure saliency in accordance with task relevance. Learning-dependent saliency increase was inferred by increased accuracy in orientation discrimination with task repetition. As a result of learning, accuracy increase was more pronounced when local and global orientation of the texture figure conflicted, and reached ceiling in both conflict and conflict-free conditions. This psychophysical effect was associated with a decrease in amplitude of negative VEP components in the configurations where global and local orientation conflicted, and to a weak increase of VEP's earliest negative component in the conflict-free condition. The VEP result is a direct demonstration that learning, in addition to increasing response of relevant channels, also reduces the weight of channels whose receptive field size and orientation tuning conflict with the task
The principle of good continuation in space and time can guide visual search in the absence of spatial priming or contextual cueing
No full textPrevious research has shown that repetition of the same target features or target spatial position over time can improve search. It has also been shown that a consistent relationship between a given target and the features or spatial arrangement of the accompanying distractors can similarly improve search. Thus it appears that the spatial and non-spatial characteristics of the target and/or the distractors are somehow retained by the visual system and used to guide visual processes such as object recognition and search. Here, we introduced a paradigm for manipulating the sequential structure of target position across trials independently of target features and contextual information. Results show that visual search is improved or impaired, respectively, when the target appears at an implicitly expected or unexpected position, according to the principle of good continuation of the target's successive positions across trials. These results are not merely due to bottom - up spatial priming, since facilitation also occurs for positions far from those recently occupied by the target, nor to contextual cueing, since the relative positions of the target and distractors are kept constant. These results demonstrate that the principle of good continuation in space and time can guide visual selective attention and ease search processes and object recognition
Acute modulation of cortical oscillatory activities during short trains of high-frequency repetitive transcranial magnetic stimulation of the human motor cortex: a combined EEG and TMS study
No full textIn this study, a combined repetitive transcranial magnetic stimulation/electroencephalography (rTMS/EEG) method was used to explore the acute changes of cortical oscillatory activity induced by intermittent short trains of high-frequency (5-Hz) rTMS delivered over the left primary motor cortex (M1). We evaluated the electrophysiological reaction to magnetic stimulation during and 2-4 s after 20 trains of 20-pulses rTMS, using event-related power (ERPow) that reflects the regional oscillatory activity of neural assemblies, and event-related coherence (ERCoh) that reflects the interregional functional connectivity of oscillatory neural activity. These event-related transformations were for the upper alpha (10-12 Hz) and beta (18-22 Hz) frequency ranges, respectively. For the alpha band, threshold rTMS and subthreshold rTMS induced an ERPow increase during the trains of stimulation mainly in frontal and central regions ipsilateral to stimulation. For the beta band, a similar synchronization of cortical oscillations for both rTMS intensities was seen. Moreover, subthreshold rTMS affected alpha-band activity more than threshold rTMS, inducing a specific ERCoh decrease over the posterior regions during the trains of stimulation. For beta band, the decrease in functional coupling was observed mainly during threshold rTMS. These findings provide a better understanding of the cortical effects of high-frequency rTMS, whereby the induction of oscillations reflects the capacity of electromagnetic pulses to alter regional and interregional synaptic transmissions of neural populations. Hum Brain Mapp, 2008. (c) 2007 Wiley-Liss, Inc
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