The spatial scale of attention strongly modulates saccade latencies.
ABSTRACT: We have previously shown that when a stimulus consisting of two concentric rings moves, saccade latencies are much longer (by 150 ms) when attention is directed to the larger ring than to the smaller ring. Here, we investigated whether this effect can be explained by a deferral of the "cost" of making a saccade while the target remains inside the attentional field, or by purely visual factors (eccentricity or contrast). We found 1) latencies were shorter when attention was directed to small features irrespective of retinal eccentricity; 2) saccade latency distributions were systematically determined by the ratio between the amplitude of the stimulus step and the diameter of the attended ring: stimulus steps that were larger than the attended ring resulted in short latencies, whereas steps smaller than the attended ring resulted in proportionally longer and more variable latencies; 3) this effect was not seen in manual reaction times to the same target movement; and 4) suprathreshold changes in the contrast of targets, mimicking possible attentional effects on perceived contrast and saliency, had little effect on latency. We argue that the spatial scale of attention determines the urgency of saccade motor preparation processes by changing the rate and rate variability of the underlying decision signal, to defer the cost of saccades that result in little visual benefit.
Project description:The ability to shift attention between relevant stimuli is crucial in everyday life and allows us to focus on relevant events. It develops during early childhood and is often impaired in clinical populations, as can be investigated in the fixation shift paradigm and the gap-overlap paradigm. Different tests use stimuli of different sizes presented at different eccentricities, making it difficult to compare them. This study systematically investigates the effect of eccentricity and target size on refixation latencies towards target stimuli. Eccentricity and target size affected attention shift latencies with greatest latencies to big targets that were presented at a small eccentricity. Slowed responses to large parafoveal targets are in line with the idea that specific areas in the superior colliculus can lead to inhibition of eye movements. Findings suggest that the two different paradigms are generally comparable, as long as the target is scaled in proportion to the eccentricity.
Project description:During natural behavior, saccades and attention act together to allocate limited neural resources. Attention is generally mediated by retinotopic visual neurons; therefore, specific neurons representing attended features change with each saccade. We investigated the neural mechanisms that allow attentional targeting in the face of saccades. Specifically, we looked for predictive changes in attentional modulation state or receptive field position that could stabilize attentional representations across saccades in area V4, known to be necessary for attention-dependent behavior. We recorded from neurons in monkeys performing a novel spatiotopic attention task, in which performance depended on accurate saccade compensation. Measurements of attentional modulation revealed a predictive attentional "hand-off" corresponding to a presaccadic transfer of attentional state from neurons inside the attentional focus before the saccade to those that will be inside the focus after the saccade. The predictive nature of the hand-off ensures that attentional brain maps are properly configured immediately after each saccade.
Project description:While numerous studies have explored the mechanisms of reward-based decisions (the choice of action based on expected gain), few have asked how reward influences attention (the selection of information relevant for a decision). Here we show that a powerful determinant of attentional priority is the association between a stimulus and an appetitive reward. A peripheral cue heralded the delivery of reward or no reward (these cues are termed herein RC+ and RC-, respectively); to experience the predicted outcome, monkeys made a saccade to a target that appeared unpredictably at the same or opposite location relative to the cue. Although the RC had no operant associations (did not specify the required saccade), they automatically biased attention, such that an RC+ attracted attention and an RC- repelled attention from its location. Neurons in the lateral intraparietal area (LIP) encoded these attentional biases, maintaining sustained excitation at the location of an RC+ and inhibition at the location of an RC-. Contrary to the hypothesis that LIP encodes action value, neurons did not encode the expected reward of the saccade. Moreover, at odds with an adaptive decision process, the cue-evoked biases interfered with the required saccade, and these biases increased rather than abating with training. After prolonged training, valence selectivity appeared at shorter latencies and automatically transferred to a novel task context, suggesting that training produced visual plasticity. The results suggest that reward predictors gain automatic attentional priority regardless of their operant associations, and this valence-specific priority is encoded in LIP independently of the expected reward of an action.
Project description:While making saccadic eye-movements to scan a visual scene, humans and monkeys are able to keep track of relevant visual stimuli by maintaining spatial attention on them. This ability requires a shift of attentional modulation from the neuronal population representing the relevant stimulus pre-saccadically to the one representing it post-saccadically. For optimal performance, this trans-saccadic attention shift should be rapid and saccade-synchronized. Whether this is so is not known. We trained two rhesus monkeys to make saccades while maintaining covert attention at a fixed spatial location. We show that the trans-saccadic attention shift in cortical visual medial temporal (MT) area is well synchronized to saccades. Attentional modulation crosses over from the pre-saccadic to the post-saccadic neuronal representation by about 50?ms after a saccade. Taking response latency into account, the trans-saccadic attention shift is well timed to maintain spatial attention on relevant stimuli, so that they can be optimally tracked and processed across saccades.
Project description:Each saccade shifts the projections of the visual scene on the retina. It has been proposed that the receptive fields of neurons in oculomotor areas are predictively remapped to account for these shifts. While remapping of the whole visual scene seems prohibitively complex, selection by attention may limit these processes to a subset of attended locations. Because attentional selection consumes time, remapping of attended locations should evolve in time, too. In our study, we cued a spatial location by presenting an attention-capturing cue at different times before a saccade and constructed maps of attentional allocation across the visual field. We observed no remapping of attention when the cue appeared shortly before saccade. In contrast, when the cue appeared sufficiently early before saccade, attentional resources were reallocated precisely to the remapped location. Our results show that pre-saccadic remapping takes time to develop suggesting that it relies on the spatial and temporal dynamics of spatial attention.
Project description:Attending to a stimulus is known to enhance the neural responses to that stimulus. Recent experiments on visual attention have shown that this modulation can have object-based characteristics, such that, when certain parts of a visual object are attended, other parts automatically also receive enhanced processing. Here, we investigated whether visual attention can modulate neural responses to other components of a multisensory object defined by synchronous, but spatially disparate, auditory and visual stimuli. The audiovisual integration of such multisensory stimuli typically leads to mislocalization of the sound toward the visual stimulus (ventriloquism illusion). Using event-related potentials and functional MRI, we found that the brain's response to task-irrelevant sounds occurring synchronously with a visual stimulus from a different location was larger when that accompanying visual stimulus was attended versus unattended. The event-related potential effect consisted of sustained, frontally distributed, brain activity that emerged relatively late in processing, an effect resembling attention-related enhancements seen at earlier latencies during intramodal auditory attention. Moreover, the functional MRI data confirmed that the effect included specific enhancement of activity in auditory cortex. These findings indicate that attention to one sensory modality can spread to encompass simultaneous signals from another modality, even when they are task-irrelevant and from a different location. This cross-modal attentional spread appears to reflect an object-based, late selection process wherein spatially discrepant auditory stimulation is grouped with synchronous attended visual input into a multisensory object, resulting in the auditory information being pulled into the attentional spotlight and bestowed with enhanced processing.
Project description:Saccadic eye movements bring events of interest to the center of the retina, enabling detailed visual analysis. This study explored whether irrelevant auditory (experiments A, B & F), visual (C & D) or tactile signals (E & F) delivered around the onset of a visual target modulates saccade latency. Participants were instructed to execute a quick saccade toward a target stepping left or right from a fixation position. We observed an interaction between auditory beeps or tactile vibrations and the oculomotor reaction that included two components: a warning effect resulting in faster saccades when the signal and the target were presented simultaneously; and a modulation effect with shorter-or longer-latencies when auditory and tactile signals were delivered before-or after-the target onset. Combining both modalities only increased the modulation effect to a limited extent, pointing to a saturation of the multisensory interaction with the motor control. Interestingly, irrelevant visual stimuli (black background or isoluminant noise strips in peripheral vision, flashed for 10 ms) increased saccade latency whether they were presented just before or after target onset. The lack of latency reduction with visual signals suggests that the modulation observed in the auditory and tactile experiments was not related to priming effects but rather to low-level audio- and tactile-visual integration. The increase in saccade latency observed with irrelevant visual stimuli is discussed in relation to saccadic inhibition. Our results demonstrate that signals conveying no information regarding where and when a visual target would appear modulate saccadic reactivity, much like in multisensory temporal binding, but only when these signals come from a different modality.
Project description:Models of visual attention hold that top-down signals from frontal cortex influence information processing in visual cortex. It is unknown whether situations exist in which visual cortex actively participates in attentional selection. To investigate this question, we simultaneously recorded neuronal activity in the frontal eye fields (FEF) and primary visual cortex (V1) during a curve-tracing task in which attention shifts are object-based. We found that accurate performance was associated with similar latencies of attentional selection in both areas and that the latency in both areas increased if the task was made more difficult. The amplitude of the attentional signals in V1 saturated early during a trial, whereas these selection signals kept increasing for a longer time in FEF, until the moment of an eye movement, as if FEF integrated attentional signals present in early visual cortex. In erroneous trials, we observed an interareal latency difference because FEF selected the wrong curve before V1 and imposed its erroneous decision onto visual cortex. The neuronal activity in visual and frontal cortices was correlated across trials, and this trial-to-trial coupling was strongest for the attended curve. These results imply that selective attention relies on reciprocal interactions within a large network of areas that includes V1 and FEF.
Project description:How attentional modulation on brain activities determines behavioral performance has been one of the most important issues in cognitive neuroscience. This issue has been addressed by comparing the temporal relationship between attentional modulations on neural activities and behavior. Our previous study measured the time course of attention with amplitude and phase coherence of steady-state visual evoked potential (SSVEP) and found that the modulation latency of phase coherence rather than that of amplitude was consistent with the latency of behavioral performance. In this study, as a complementary report, we compared the time course of visual attention shift measured by event-related potentials (ERPs) with that by target detection task. We developed a novel technique to compare ERPs with behavioral results and analyzed the EEG data in our previous study. Two sets of flickering stimulus at different frequencies were presented in the left and right visual hemifields, and a target or distracter pattern was presented randomly at various moments after an attention-cue presentation. The observers were asked to detect targets on the attended stimulus after the cue. We found that two ERP components, P300 and N2pc, were elicited by the target presented at the attended location. Time-course analyses revealed that attentional modulation of the P300 and N2pc amplitudes increased gradually until reaching a maximum and lasted at least 1.5 s after the cue onset, which is similar to the temporal dynamics of behavioral performance. However, attentional modulation of these ERP components started later than that of behavioral performance. Rather, the time course of attentional modulation of behavioral performance was more closely associated with that of the concurrently recorded SSVEPs analyzed. These results suggest that neural activities reflected not by either the P300 or N2pc, but by the SSVEPs, are the source of attentional modulation of behavioral performance.
Project description:Presenting a behaviorally irrelevant cue shortly before a target at the same location decreases the latencies of saccades to the target, a phenomenon known as exogenous attention facilitation. It remains unclear whether exogenous attention interacts with early, sensory stages or later, motor planning stages of saccade production. To distinguish between these alternatives, we used a saccadic adaptation paradigm to dissociate the location of the visual target from the saccade goal. Three male and four female human subjects performed both control trials, in which saccades were made to one of two target eccentricities, and adaptation trials, in which the target was shifted from one location to the other during the saccade. This manipulation adapted saccades so that they eventually were directed to the shifted location. In both conditions, a behaviorally irrelevant cue was flashed 66.7 ms before target appearance at a randomly selected one of seven positions that included the two target locations. In control trials, saccade latencies were shortest when the cue was presented at the target location and increased with cue-target distance. In contrast, adapted saccade latencies were shortest when the cue was presented at the adapted saccade goal, and not at the visual target location. The dynamics of adapted saccades were also altered, consistent with prior adaptation studies, except when the cue was flashed at the saccade goal. Overall, the results suggest that attentional cueing facilitates saccade planning rather than visual processing of the target.