PURPOSE:In this study we investigated in observers with low myopia: (i) the pattern of lateral interactions between stimuli activating early cortical analyzers and its modulation by perceptual learning (PL), and (ii) whether PL transferred to untrained stimuli and tasks and whether it exhibits interocular transfer.METHOD:Participants (seven adults with low myopia) performed 12 training sessions. Participants were trained on a contrast detection task of a central Gabor target flanked by two co-oriented and co-aligned high contrast Gabor patches. Target-to-flankers separation along the vertical axis was varied from 2 wavelengths (λ) to 8λ.RESULTS:The results showed that before PL facilitatory lateral interactions in the myopic eye were reduced in strength, but PL increased contrast sensitivity and improved facilitatory lateral interactions. However, PL did not transfer to different local/global orientations and lower spatial frequencies. On the other hand, PL resulted in an enhancement of the contrast sensitivity function (CSF) and of the uncorrected visual acuity (UCVA) both in the trained and untrained eye.CONCLUSIONS:Such improvements seem to be associated to a modulation of lateral interactions between target and flankers and it is likely to take place at a level in which the inputs from the two eyes converge.

The aim of this study was to estimate the effects on working memory efficiency of interference control mechanisms that act during selective attention on the perception of external stimuli (access) as well as the mechanisms that operate on internal representations of this memory system (deletion). These effects were examined as a function of task difficulty by increasing the memory load. Working memory performance was evaluated when access and deletion functions were active and under noninterference conditions. Subjects were able to efficiently apply the access and deletion functions during trials of low or moderate difficulty, but during trials of high difficulty, they were only able to apply the access functions and failed to activate the deletion functions. These results provide evidence supporting the independency of each of these interference control functions. Only the ability to control interference from internal memory representations is vulnerable to task difficulty and is predictive of working memory performance.

Working memory decay in advanced age has been attributed to a concurrent decrease in the ability to control interference. The present study contrasted a form of interference control in selective attention that acts upon the perception of external stimuli (access) with another form that operates on internal representations in working memory (deletion), in order to determine both of their effects on working memory efficiency in younger and older adults. Additionally, we compared memory performance under these access and deletion functions to performance in their respective control conditions. The results indicated that memory accuracy improved in both age groups from the access functions, but that only young adults benefited from the deletion functions. In addition, intrusion effects in the deletion condition were larger in older than in younger adults. The ability to control the irrelevant perception- and memory-elicited interference did not decline in general with advancing age; rather, the control mechanisms that operate on internal memory representations declined specifically.

The effect of visual experience is usually investigated through active (task dependent) training in a discrimination task. In contrast, the current work explored the psychophysical and electrophysiological correlates of passive (task independent) visual experience in texture segmentation by using an inattentional blindness-like paradigm (Mack et al., 1992). The psychophysical and electrophysiological responses to a segmented line-texture bar, with texture elements oriented either congruently (parallel) or noncongruently (orthogonal) to bar orientation, were collected after both short and long passive experience, with the texture presented on the background while subjects performed a primary task. Subjects were not able to distinguish the orientation of the bar (psychophysical results) after either short or long passive experience. However, the short experience produced an electrophysiological correlate of texture segmentation (N150), and the amplitude of this component was greater for the parallel bar, demonstrating that it reflected not simply local orientation discontinuities but also texture boundary-surface orientation congruency. This configurational effect in texture segmentation, which occurred without awareness during passive viewing, disappeared when the subjects had previously discriminated the orientation of the bar and when experience was lengthened, probably as a consequence of adaptation. Our study provides the first ERP evidence that boundary-surface relations are available during short passive visual experiences of very salient texture images and are suppressed by long experience, probably because of adaptation.

We previously showed that actively practising to discriminate the orientation of a line-texture bar increases its saliency and modulates the ERP-component amplitudes reflecting texture segmentation, suggesting that increased saliency results from inhibition of incongruent local orientation (orthogonal to the bar) (Casco et al., 2004). We now show an experience-dependent increase of saliency even when the texture is an irrelevant background to a central task engaging subject's attention. However, this improved perception in single randomly chosen target trials (Mack, Tang, Tuma, Kahn and Rock, 1992) does not occur in the two groups where, unexpectedly, orientation discrimination of the bar was asked either at the beginning (50% accuracy) or at the end (60% accuracy) of the 300-trials block. Instead, the group for whom the target trial was presented in a second block executed with a delay of several hours and at least one night's sleep showed a significant increase of saliency (72.5 % accuracy) but only when local elements were congruent to the global orientation of the bar. If the elements were incongruent, accuracy dropped to 41%, indicating that increased saliency relies on a larger response to local orientation within the bar. The electrophysiological correlate of this task-irrelevant improvement is a selective ERP modulation on the second day, consisting in a significant increase in the segmentation-component amplitude, but only when elicited by the congruent bar condition. These results show that perceptual learning may not require attention to be directed on the stimulus. Task-relevant and task-irrelevant learning involve different mechanisms: the former based on inhibition of information irrelevant to the task (Casco et al., 2004) and leading to explicit figure-ground segmentation, the latter based on enhancement of response to local orientation in the texture bar, also resulting in figure-ground segmentation.

In contrast to the classical distinction between a controlled orienting of attention induced by central cues and an automatic capture induced by peripheral cues, recent studies suggest that central cues, such as eyes and arrows, may trigger a reflexive-like attentional shift. Yet, it is not clear if the attention shifts induced by these two cues are similar or if they differ in some important aspect. To answer this question, in Experiment 1 we directly compared eye and arrow cues in a counter-predictive paradigm while in Experiment 2 we compared the above cues with a different symbolic cue. Finally, in Experiment 3 we tested the role of over-learned associations in cueing effects. The results provide evidence that eyes and arrows induce identical behavioural effects. Moreover, they show that over-learned associations between spatially neutral symbols and the cued location play an important role in yielding early attentional effects.

Gestalt factors of collinearity and similarity facilitate two fundamental perceptual tasks: grouping elements into figures and segmentation of figures from the ground. We have used a global-local paradigm to examine the psychophysical and neural correlates of these processes in humans: observers discriminated between orientations of either a three-Gabor group (grouping), or of a central Gabor within the group (segmentation). Groups were centered on a background of differently oriented Gabors. In both tasks, accuracy was increased by the collinearity (Experiment 1) and similarity (Experiment 2) of elements within the three-Gabor group. ERP correlates of facilitation differed across tasks. For segmentation, they were indexed by increased amplitude of negative ERP components, specific for processing textures, peaking at 75-250 and 150-250 ms, respectively. For grouping, collinearity and similarity had different effects. Collinearity produced a positive polarity deflection between 40 and 179 ms (i.e. the opposite to segmentation). This task-dependent switch in sign of polarity change, without corresponding changes in the stimulus or perception, reflects distinct neural mechanisms for collinear facilitation in grouping and segmentation. In contrast, similarity reduced positivity at 275 ms. Results show similar modulation of segmentation components via the distinct mechanism underlying collinearity and similarity, but distinct modulation of grouping components via collinearity and similarity.

To find the diagnostic spatial frequency information in different painting styles (cubism, impressionism and realism), we have compared sensitivity (d') in distinguishing signal (subject of the painting) from noise with normal, high-pass and low-pass filtered images at long (150 ms) and short (30 ms) exposure. We found that for cubist-style images, d' increases with high-pass filtering compared with normal and low-pass filtered images, but decreases with low-pass filtering compared with normal images. These results indicate that channels with high spatial resolution provide the diagnostic information to solve the binding problem. Sensitivity for images in impressionist style was instead reduced by both low- and high-pass filtering. This indicates that both high and low spatial frequency channels play a role in solving the binding problem, suggesting the involvement of large collator units that group the response of small channels tuned to the same orientation. The difference between realism, which shows higher sensitivity for low-frequency filtering at short durations and cubism in which the binding problem is solved by high spatial frequency channels, has a corresponding difference in aesthetic judgment: the probability of judging a painting as 'intriguing' is larger with low-pass filtering than with high-pass filtering in realism, while the opposite is true for cubism. This suggests that the aesthetic experience is available during early processing of an image, and could preferentially influence high-level categorization of the subject of a painting.

Exogenous orienting has been widely studied by using peripheral cues whereas endogenous orienting has been studied with directional central cues. However, recent evidence has shown that centrally presented eye-gaze and arrows may produce an automatic rather than voluntary orienting of attention. Therefore, the aim of the present study was to investigate the behavioural and electrophysiological (event-related potentials—ERP) correlates of the attentional shift induced by arrows and eye-gaze. In order to have a control condition, we compared arrows and eye-gaze with a purely endogenous cue, i.e., a texture arbitrarily coding one direction. We analyzed the ERP components (P1, N1, P2a, P2p, P3) elicited by the cue stimuli and the early lateralised attentional effect (early directing attention negativity—EDAN). In addition, in order to investigate the topography of the neural mechanisms underlying the cortical activity in each cueing condition, we applied a temporal segmentation procedure. The results showed that the three cueing conditions induced a different strength of activation within the same cortical network. Occipito-parietal regions were involved in the early processing of visual information, followed by an involvement of frontal areas, likely implicated in learning associations. These data confirm the assumption that, in contrast to purely endogenous cues, arrows and eye-gaze induce a very fast attentional shift. However, the similarity of the ERP components and of the topographical cortical maps among conditions suggest that this early orienting of attention is more likely related to an overlearned association mechanism rather than to a real exogenous attentional process.