Biology subjects

Hanning, N. M.

Publications and source records attributed to Hanning, N. M..

15 recordsLinked to original sources

bioRxiv2026

Transcranial magnetic stimulation to frontal cortex, unlike occipital stimulation, does not disrupt exogenous attention

Orienting covert attention to a target location improves performance across a wide array of visual tasks [1, 2]. Whereas fMRI studies have identified partially overlapping frontoparietal networks underlying endogenous (voluntary) and exogenous (involuntary) covert attention, these correlational methods cannot establish whether a given region is functionally necessary. Prior neurostimulation studies have established that early visual cortex (V1/V2) is critical for exogenous [3, 4] but not endogenous attention [5], whereas the right frontal eye field (rFEF+) is critical for endogenous attention [5]. Here, we used a combined psychophysical-TMS protocol to investigate whether rFEF+ is also required for exogenous attention. Participants performed an orientation discrimination task, in which a peripheral cue (valid, neutral, or invalid) preceded a target and a distractor stimulus. We applied two successive TMS pulses to rFEF+ during stimulus presentation and measured contrast-response functions (CRFs) to quantify perceptual sensitivity (d') across all attention cueing and stimulation conditions. When the distractor was stimulated, exogenous attention yielded a characteristic response gain at the target--with performance benefits for valid cues and costs for invalid cues at high contrast levels. Crucially, this response gain was entirely preserved when the target was stimulated. This pattern contrasts with previous findings demonstrating that TMS to V1/V2 eliminates exogenous attentional effects at the stimulated location. These results indicate that rFEF+ is not necessary for exogenous attention, and together with previous studies [3-5] complete a double dissociation: rFEF+ is critical for endogenous but not exogenous attention, whereas V1/V2 is critical for exogenous but not endogenous attention. These findings reveal a distinct causal cortical architecture for voluntary and involuntary spatial attention, suggesting that they rely on different cortical scaffolds.

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bioRxiv2024

An Information Processing Pattern from Robotics Predicts Properties of the Human Visual System

We tested the hypothesis that an algorithmic information processing pattern from robotics, Active InterCONnect (AICON), could serve as a useful representation for exploring human vision. We created AICON-based computational models for two visual illusions: the shape-contingent color aftereffect and silencing by motion. The models reproduced the effects seen in humans and generated surprising and novel predictions that we validated through human psychophysical experiments. Inconsistencies between model predictions and experimental results were resolved through iterative model adjustments. For the shape-contingent color aftereffect, the model predicted and experiments confirmed weaker aftereffects for outline shape manipulations and individual differences in perceived aftereffects. For silencing by motion, the model predicted and experiments validated unexpected trends as well as individual differences. Our findings demonstrate AICONs ability to capture relevant aspects of human visual information processing including variability across individuals. It highlights the potential for novel collaborations between synthetic and biological disciplines.

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bioRxiv2023

Presaccadic attention enhances and reshapes the Contrast Sensitivity Function around the visual field

Contrast sensitivity, which constrains our vision, decreases from fovea to periphery, from the horizontal to the vertical meridian, and from the lower vertical to the upper vertical meridian. The Contrast Sensitivity Function (CSF) depicts how contrast sensitivity varies with spatial frequency (SF). To overcome these visual constraints, we constantly make saccadic eye movements to foveate on relevant objects in the scene. Already before saccade onset, presaccadic attention shifts to the saccade target and enhances perception. However, it is unknown whether and how it modulates the interplay between contrast sensitivity and SF, and if this effect varies around polar angle locations. Contrast sensitivity enhancement may result from a horizontal or vertical shift of the CSF, increase in bandwidth, or any combination. Here, we investigated these possibilities by extracting key attributes of the CSF using Hierarchical Bayesian Modeling, which enables precise estimation of the CSF parameters by decomposing the variability of the dataset into multiple levels. The results reveal that presaccadic attention (1) enhances contrast sensitivity across SF, (2) increases the most preferred and the highest discernable SF, and (3) narrows the bandwidth. Therefore, presaccadic attention bridges the gap between presaccadic and post-saccadic input by increasing visibility at the saccade target. Counterintuitively, the presaccadic enhancement in contrast sensitivity was more pronounced where perception is better -along the horizontal than the vertical meridian- exacerbating polar angle asymmetries. Our results call for an investigation of the differential neural modulations underlying presaccadic perceptual changes for different saccade directions. Significance statementThe contrast sensitivity function (CSF) describes how our ability to perceive contrast depends on spatial frequency. Contrast sensitivity is highest at the fovea and decreases in the periphery, especially at vertical locations. We thus make saccadic eye movements to view objects in detail. Already before moving our eyes, presaccadic attention enhances perception at the target location. But how does it influence the interplay between spatial frequency and contrast sensitivity, and does its effect vary around the visual field? Using Hierarchical Bayesian Modeling, we show that presaccadic attention enhances and reshapes the CSF to prepare the periphery for upcoming fixation. Counterintuitively, it does so more at horizontal locations where vision is stronger, suggesting smoother perception across horizontal than vertical eye movements.

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bioRxiv2023

EasyEyes - Accurate fixation for online vision testing of crowding and beyond

Online methods allow testing of larger, more diverse populations, with much less effort than in-lab testing. However, many psychophysical measurements, including visual crowding, require accurate eye fixation, which is classically achieved by testing only experienced observers who have learned to fixate reliably, or by using a gaze tracker to restrict testing to moments when fixation is accurate. Alas, both approaches are impractical online since online observers tend to be inexperienced, and online gaze tracking, using the built-in webcam, has a low precision ({+/-}4 deg, Papoutsaki et al., 2016). The EasyEyes open-source software reliably measures peripheral thresholds online with accurate fixation achieved in a novel way, without gaze tracking. EasyEyes tells observers to use the cursor to track a moving crosshair. At a random time during successful tracking, a brief target is presented in the periphery. The observer responds by identifying the target. To evaluate EasyEyes fixation accuracy and thresholds, we tested 12 naive observers in three ways in a counterbalanced order: first, in the lab, using gaze-contingent stimulus presentation (Kurzawski et al., 2023; Pelli et al., 2016); second, in the lab, using EasyEyes while independently monitoring gaze; third, online at home, using EasyEyes. We find that crowding thresholds are consistent (no significant differences in mean and variance of thresholds across ways) and individual differences are conserved. The small root mean square (RMS) fixation error (0.6 deg) during target presentation eliminates the need for gaze tracking. Thus, EasyEyes enables fixation-dependent measurements online, for easy testing of larger and more diverse populations.

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bioRxiv2023

The Extrafoveal Preview Effect is More Pronounced Where Perception is Poor

The pre-saccadic preview of a peripheral target enhances the efficiency of its post-saccadic processing, termed the extrafoveal preview effect. Peripheral visual performance -and thus the quality of the preview- varies around the visual field, even at iso-eccentric locations: it is better along the horizontal than vertical meridian and along the lower than upper vertical meridian. To investigate whether these polar angle asymmetries influence the preview effect, we asked human participants (to preview four tilted gratings at the cardinals, until a central cue indicated to which one to saccade. During the saccade, the target orientation either remained or slightly changed (valid/invalid preview). After saccade landing, participants discriminated the orientation of the (briefly presented) second grating. Stimulus contrast was titrated with adaptive staircases to assess visual performance. Expectedly, valid previews increased participants post-saccadic contrast sensitivity. This preview benefit, however, was inversely related to polar angle perceptual asymmetries; largest at the upper, and smallest at the horizontal meridian. This finding reveals that the visual system compensates for peripheral asymmetries when integrating information across saccades, by selectively assigning higher weights to the less-well perceived preview information. Our study supports the recent line of evidence showing that perceptual dynamics around saccades vary with eye movement direction. Significance StatementWe constantly make saccadic eye movements to bring relevant visual information into the fovea, which has the highest acuity. Before each saccade, we use "previewed" peripheral information to support our post-saccadic vision. Our sensitivity varies around the visual field -at the same eccentricity it is best along the horizontal meridian and worst at the upper vertical meridian. An optimal visual system should rely more on previewed information with higher precision. Our study reveals the opposite: peripheral preview shapes subsequent post-saccadic foveal processing more at locations where peripheral vision is worse. This finding implies that the human visual system compensates for sensitivity differences around the visual field when integrating information across eye movements.

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bioRxiv2023

Dissociable roles of human frontal eye fields and early visual cortex in presaccadic attention -- evidence from TMS

Shortly before each saccadic eye movement, presaccadic attention improves visual sensitivity at the saccade target1-5 at the expense of lowered sensitivity at non-target locations6-11. Some behavioral and neural correlates of presaccadic attention and covert attention -which likewise enhances sensitivity, but during fixation12-are similar13. This resemblance has led to the debatable13-18 notion that presaccadic and covert attention are functionally equivalent and rely on the same neural circuitry19-21. At a broad scale, oculomotor brain structures (e.g., FEF) are also modulated during covert attention22-24 - yet by distinct neuronal subpopulations25-28. Perceptual benefits of presaccadic attention rely on feedback from oculomotor structures to visual cortices29,30 (Fig. 1a); micro-stimulation of FEF in non-human primates affects activity in visual cortex31-34 and enhances visual sensitivity at the movement field of the stimulated neurons35-37. Similar feedback projections seem to exist in humans: FEF+ activation precedes occipital activation during saccade preparation38,39 and FEF TMS modulates activity in visual cortex40-42 and enhances perceived contrast in the contralateral hemifield40. We investigated presaccadic feedback in humans by applying TMS to frontal or visual areas during saccade preparation. By simultaneously measuring perceptual performance, we show the causal and differential roles of these brain regions in contralateral presaccadic benefits at the saccade target and costs at non-targets: Whereas rFEF+ stimulation reduced presaccadic costs throughout saccade preparation, V1/V2 stimulation reduced benefits only shortly before saccade onset. These effects provide causal evidence that presaccadic attention modulates perception through cortico-cortical feedback and further dissociate presaccadic and covert attention. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/529691v2_fig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@1567165org.highwire.dtl.DTLVardef@2ecec9org.highwire.dtl.DTLVardef@10a00adorg.highwire.dtl.DTLVardef@1b29dfd_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1.C_FLOATNO Background and experimental design. (a) Feedback connections originally established in non-human primates29,30,36,90,104,105 assumed to underly perceptual correlates of human presaccadic attention. FEF: Frontal eye field, SC: Superior Colliculus; (b) Response gain effect of presaccadic attention on the contrast response function: presaccadic attention scales the response by a multiplicative gain factor, resulting in an increase of the asymptotic response dmax (the maximal response achieved at high contrast)9,48. (c) Determining occipital (V1/V2) stimulation sites (Exp.1 & 2a) and stimulus placement for both experiments via phosphene mapping: Observers were stimulated laterally around the occipital pole until they perceived a phosphene (in the contralateral visual field), then drew its outline on the screen. The center of the phosphene drawings (stimulated region) and the symmetric region (not stimulated) were used for stimulus placement in the main experiment, where we applied sub-phosphene-threshold TMS using identical coil positioning. (d) Determining rFEF+ stimulation sites (Exp.2b). rFEF+ (yellow ROI) was localized on each individual observers anatomy (two exemplary observers shown here) via a probabilistic topography atlas76 and verified by anatomical landmarks (junction of the precentral and superior frontal sulcus; light gray areas)64,65,67. (e) Presaccadic orientation discrimination task. After a fixation period, a central direction cue (black line) appeared. Observers were instructed to make a saccade to the indicated target marked by placeholder dots. Note that the saccade was equally likely directed to the stimulated and to the symmetric region / hemifield. 100ms after cue onset, a tilted test Gabor patch was presented at either the saccade target (valid; 50%) or at the opposite location (invalid), randomly intermixed; a vertical Gabor was presented at the other location. Importantly, stimuli were presented during saccade preparation, i.e., while gaze was still at the screen center. After saccade offset, a response cue (white dots on placeholder) indicated the location at which the test Gabor had appeared, and observers reported its orientation. In the neutral condition (separately blocked) the cue pointed to both placeholders and observers kept fixating (supplemental Video S1 demonstrates the trials sequence of each condition). (f) Trial timeline. Observers received double-pulse TMS (50ms inter-pulse interval) locked to stimuli onset (Exp.1) or at various times during saccade preparation (0-200ms relative to cue onset; Exp.2). Whereas grating contrast was varied to measure contrast response functions in Exp.1, contrast was fixed to 46% in Exp.2. (g) Experimental conditions. The test was equally likely presented at the stimulated region (test stimulated) or in the opposite hemifield (not stimulated). Moreover, the test was equally likely presented at the saccade target (valid) or opposite of it (invalid). Note that the fixation condition (neutral) was only tested in Exp.1. C_FIG

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bioRxiv2022

Presaccadic attention depends on eye movement direction

With every saccadic eye movement, humans bring new information into their fovea to be processed with high visual acuity. Notably, perception is enhanced already before a relevant item is foveated: During saccade preparation, presaccadic attention shifts to the upcoming fixation location, which can be measured via behavioral correlates such as enhanced visual performance or modulations of sensory feature tuning. The coupling between saccadic eye movements and attention is assumed to be robust and mandatory, and considered a mechanism facilitating the integration of pre- and post-saccadic information. However, until recently it had not been investigated as a function of saccade direction. Here, we measured contrast response functions during fixation and saccade preparation in male and female observers and found that the pronounced response gain benefit typically elicited by presaccadic attention is selectively lacking before upward saccades at the group level - some observers even showed a cost. Individual observers sensitivity before upward saccades was negatively related to their amount of surface area in primary visual cortex representing the saccade target, suggesting a potential compensatory mechanism that optimizes the use of the limited neural resources processing the upper vertical meridian. Our results raise the question how perceptual continuity is achieved and upward saccades can be accurately targeted despite the lack of - theoretically required- presaccadic attention. Significance StatementWhen we make a saccadic eye movement to a target location in the visual field, perception improves at the saccade target, already before the eyes start moving. This benefit afforded by presaccadic attention is thought to be mandatory and independent of eye movement direction. We show that this is not the case; moving our eyes horizontally or downwards, but not upwards, enhances contrast sensitivity. At the neural level, however, humans with less V1 cortical tissue representing the target location for upwards saccades have some presaccadic enhancement. The finding that presaccadic attention is dependent upon eye movement direction challenges the view that the presaccadic benefit is automatic and mandatory in nature.

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bioRxiv2022

Presaccadic attention sharpens visual acuity

Visual perception is limited by spatial resolution, which declines with eccentricity and differs around polar angle locations. To compensate for poor peripheral resolution, we make rapid eye movements -saccades- to bring peripheral objects into high-acuity foveal vision. Already before saccade onset, visual attention shifts to the saccade target location and prioritizes visual processing. This presaccadic shift of attention improves performance in many visual tasks, but whether it changes resolution is unknown. Here, we investigated whether presaccadic attention sharpens peripheral spatial resolution; and if so, whether such effect interacts with polar angle locations. We measured acuity thresholds in an orientation discrimination task during fixation and saccade preparation around the visual field. The results revealed that presaccadic attention sharpens acuity, which can facilitate a smooth transition from peripheral to foveal representation. This acuity enhancement is similar across the four cardinal locations; thus, presaccadic attention does not change polar angle differences in resolution.

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bioRxiv2022

Transcranial magnetic stimulation to frontal but not occipital cortex disrupts endogenous attention

Covert endogenous (voluntary) attention improves visual performance. Human neuroimaging studies suggest that the putative human homolog of macaque FEF (FEF+) is critical for this improvement, whereas early visual areas are not. Yet, MRI methods are correlational, as they do not manipulate brain function. Here we investigated whether rFEF+ or V1/V2 play a causal role in endogenous attention. We used transcranial magnetic stimulation (TMS) to alter activity in visual cortex (Exp.1) or rFEF+ (Exp.2) when observers performed an orientation discrimination task while attention was manipulated. On every trial, they received double-pulse TMS at a predetermined site (stimulated region) around the occipital pole or the rFEF+. Two cortically magnified gratings were presented, one in the stimulated region (contralateral to the stimulated cortical area) and another in the symmetric (ipsilateral) non-stimulated region. Grating contrast was varied to measure contrast response functions (CRFs) for all attention and stimulation combinations. In Exp.1, the CRFs were similar at the stimulated and non-stimulated regions, indicating that early visual areas do not modulate endogenous attention during stimulus presentation. In contrast, occipital TMS eliminates exogenous (involuntary) attention effects on performance (1). In Exp.2, rFEF+ stimulation decreased the overall attentional effect; neither benefits at the attended location nor cost at the unattended location were significant. This pattern is mimicked in the frequency and directionality of microsaccades: Whereas occipital stimulation did not affect microsaccades, rFEF+ stimulation caused a higher microsaccade rate selectively directed toward the stimulated hemifield. These results provide causal evidence of the role of this frontal region for endogenous attention. SIGNIFICANCE STATEMENTHuman neuroimaging studies have revealed activity in frontal regions (e.g., FEF+) as a neural correlate of endogenous (voluntary) attention, and early visual areas (V1/V2) as neural correlates of both endogenous and exogenous (involuntary) attention. Using a causal manipulation-transcranial magnetic stimulation-we show that briefly disrupting activity in rFEF+ weakens endogenous attentions benefits at attended and costs at unattended locations. In contrast, V1/V2 stimulation did not alter endogenous attention (although we have previously demonstrated that it eliminates effects of exogenous attention). Correspondingly, whereas stimulation to rFEF+ increased the rate of microsaccades directed toward the stimulated hemifield, occipital stimulation did not. Together, these results provide causal evidence for the role of rFEF+ but not V1/V2 in endogenous attention.

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bioRxiv2022

Where we perceive before we look: The distribution of presaccadic attention assessed with dynamic 1/f noise

Already before the onset of a saccadic eye movement, we preferentially process visual information at the upcoming eye fixation. This presaccadic shift of attention is typically assessed via localized test items, which potentially bias the attention measurement. Here we show how presaccadic attention shapes perception from saccade origin to target when no scene-structuring items are presented. Participants made saccades into a 1/f ("pink") noise field, in which we embedded a brief orientation signal at various locations shortly before saccade onset. Local orientation discrimination performance served as a proxy for the allocation of attention. Results demonstrate that (1) saccades are preceded by shifts of attention to their goal location even if they are directed into an unstructured visual field, but the spread of attention, compared to target-directed saccades, is broad; (2) the presaccadic attention shift is accompanied by considerable attentional costs at the presaccadic eye fixation; (3) objects markedly shape the distribution of presaccadic attention - demonstrating the relevance of an item-free approach for measuring attentional dynamics across the visual field.

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bioRxiv2021

Presaccadic attention enhances contrast sensitivity, but not at the upper vertical meridian

Human visual performance is not only better at the fovea and decreases with eccentricity, but also has striking radial asymmetries around the visual field: At a fixed eccentricity, it is better along (1) the horizontal than vertical meridian and (2) the lower than upper vertical meridian. These asymmetries are not alleviated by covert exogenous or endogenous attention, but have been studied exclusively during eye fixation. However, a major driver of everyday attentional orienting is saccade preparation, during which visual attention automatically shifts to the future eye fixation. This presaccadic shift of attention is considered strong and compulsory, and relies on fundamentally different neural computations and substrates than covert attention. Given these differences, we investigated whether presaccadic attention can compensate for the ubiquitous performance asymmetries observed during eye fixation. Our data replicate polar performance asymmetries during fixation and document the same asymmetries during saccade preparation. Crucially, however, presaccadic attention enhanced contrast sensitivity at the horizontal and lower vertical meridian, but not at the upper vertical meridian. Thus, instead of attenuating polar performance asymmetries, presaccadic attention exacerbates them.

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bioRxiv2021

A dynamic pink noise paradigm to assess spatial-temporal attention without biasing perceptual processing

Psychophysical paradigms measure visual attention via localized test items to which observers must react or whose features have to be discriminated. These items, however, potentially interfere with the intended measurement as they bias observers spatial and temporal attention to their location and presentation time. Furthermore, visual sensitivity for conventional test items naturally decreases with retinal eccentricity, which prevents direct comparison of central and peripheral attention assessments. We developed a stimulus that overcomes these limitations. A brief oriented discrimination signal is seamlessly embedded into a continuously changing 1/f noise field, such that observers cannot anticipate potential test locations or times. Using our new protocol, we demonstrate that local orientation discrimination accuracy for 1/f filtered signals is largely independent of retinal eccentricity. Moreover, we show that items present in the visual field indeed shape the distribution of visual attention, suggesting that classical studies investigating the spatiotemporal dynamics of visual attention via localized test items may have obtained a biased measure. We recommend our protocol as an efficient method to evaluate the behavioral and neurophysiological correlates of attentional orienting across space and time. Significance statementWhere (and when) we pay attention can be experimentally quantified via visual sensitivity: Attending to a certain visual signal results in better detection and feature discrimination performance. This approach is widely used, but poses an unrecognized dilemma: The test signal itself, typically a grating or letter stimulus, biases observers perception and expectations - and thus also the attention measurement. We developed a stimulus that manages without test items. The signal to measure attention is seamlessly embedded in a dynamic 1/f noise field, so that neither spatial nor temporal information about signal presentation is conveyed. Unlike with conventional approaches, perception and expectations in this new protocol remain unbiased, and the undistorted spatial and temporal spread of visual attention can be measured.

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bioRxiv2020

Eye and hand movements disrupt attentional control

Voluntary attentional control is the ability to selectively focus on a subset of visual information in the presence of other competing stimuli. While it is well established that this capability is a marker of cognitive control that allows for flexible, goal-driven behavior, it is still an open question how robust it is. In this study we contrasted voluntary attentional control with the most frequent source of automatic, involuntary attentional orienting in daily life--shifts of attention prior to goal-directed eye and hand movements. In a multi-tasking paradigm, we asked participants to attend at a location while planning eye or hand movements elsewhere. We observed that voluntary attentional control suffered with every simultaneous action plan. Crucially, this impairment occurred even when we reduced task difficulty and memory load--factors known to interfere with attentional control. Furthermore, the performance cost was limited to voluntary attention. We observed simultaneous attention benefits at two movement targets without attentional competition between them. This demonstrates that the visual system allows for the concurrent representation of multiple attentional foci. It further reveals that voluntary attentional control is extremely fragile and dominated by automatic, premotor shifts of attention. We propose that action-driven selection disrupts voluntary attention and plays a superordinate role for visual selection.

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bioRxiv2020

Attention capture outside the oculomotor range

Neurophysiological studies demonstrated that attentional orienting is performed by fronto-parietal brain areas which also play an important role in oculomotor control. Accordingly, several studies claimed that exogenous attention can only be allocated to where we can potentially make an eye movement, i.e. within the oculomotor range. We tested this assumption by assessing the disruptive effect of a salient distractor at locations within and beyond participants oculomotor range. Participants rotated their heads ~38{degrees} leftwards to prevent them from performing large rightward saccades. In this posture, participants fixated the screen center and focused their attention on a location on the left side of the screen, where they had to discriminate the orientation of a visual noise patch. While assessing visual orientation sensitivity - an established proxy of visual attention - at this endogenously attended location, we flashed a salient cue either at the attended location or at various locations inside or outside their oculomotor range. We found that whenever the salient cue occurred at a location other than the endogenously attended location, it withdrew visual attention and significantly disrupted endogenous attentional orienting. Crucially, this effect occurred regardless of whether the cue was presented within or beyond participants oculomotor range, demonstrating that exogenous events equally grab our attention both inside and outside the eyes reach. Since spatial exogenous attention was attracted unrestrictedly toward locations to which no saccade could be executed, the coupling of attention and eye movement control is less tight than, for example, the prominent "Premotor Theory of Attention" suggests. Rather, attention can be shifted freely over the entire visual range, independent of pathological and physiological limitations of the eye movement system.

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bioRxiv2020

Theory of Visual Attention (TVA) in Action: Assessing Premotor Attention in Simultaneous Eye-Hand Movements

Attention shifts that precede goal-directed eye and hand movements are regarded as markers of motor target selection. Whether effectors compete for a single, shared attentional resource during simultaneous eye-hand movements or whether attentional resources can be allocated independently towards multiple target locations is controversially debated. Independent, effector-specific target selection mechanisms underlying parallel allocation of visuospatial attention to saccade and reach targets would predict an increase of the overall attention capacity with the number of active effectors. We test this hypothesis in a modified Theory of Visual Attention (TVA; Bundesen, 1990) paradigm. Participants reported briefly presented letters during eye, hand, or combined eye-hand movement preparation to centrally cued locations. Modeling the data according to TVA allowed us to assess both the overall attention capacity and the deployment of visual attention to individual locations in the visual work space. In two experiments, we show that attention is predominantly allocated to the motor targets - without pronounced competition between effectors. The parallel benefits at eye and hand targets, however, have concomitant costs at non-motor locations, and the overall attention capacity does not increase by the simultaneous recruitment of both effector systems. Moreover, premotor shifts of attention dominate over voluntary deployment of processing resources, yielding severe impairments of voluntary attention allocation. We conclude that attention shifts to multiple effector targets without mutual competition given that sufficient processing resources can be withdrawn from movement-irrelevant locations.

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