Selective Attention Within the Foveola

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© 2017 Nature America, Inc., part of Springer Nature. All rights reserved. York, USA. Correspondence should be addressed to M.P. ( M.P. to addressed be should Correspondence USA. York, Massachusetts, USA. 1 as 1), in (experiment parafovea in the task a detection by conducting baseline a established study, first we this In processing. of speed and of on discriminability and its effects of control gaze center at very the attention fine and deployment selective the examined that ments overcome been now have challenges these But foveola. the within attention covert tigate sight of line the tion posi precisely movements eye the microscopic as that well observation as recent areas, cortical extrastriate and striate in fovea the to This is proposal the large considering feasible representation devoted could raised been attention also has gaze of covert center the around beneficial of be control high-resolution that possibility foveola the of subregions within mation infor process to that selectively of is coarse attention too scale spatial the assumed commonly is it Furthermore, scale. this at unclear is responses overt and covert between distinction conceptual the that fixationfoveoladuring the acrossstimuliincessantly move eye of In movements small field. portion side this the addition, visual out resources neural focuses that as a process regarded traditionally looking’ is observer the ‘where with tified region is This anatomical iden commonly foveola sense. little makes at arm’s fingernail length. index the of size the densely packed, an area that covers only ~1° of visual angle most are cones where fovea the of region capillary-free and rod- the gaze of center the at retina the of region high-acuity the foveola, the outside far and is, eccentricity)—that (5°–10°) of (>10° periphery perifovea the in mostly and (1°–5°) parafovea the in saccade preparation times reaction trast sensitivity and spatial resolution, speeds information accrual and con increases resources attentional of allocation covert advantages, many its Among perception. visual for essential is attention Covert global mechanism that exerts its action across the entire visual field. in fine spatial vision. They show that the commonly studied covert shifts of attention away from the fovea are the expression of a fraction of a degree apart within the foveola. These findings reveal a surprisingly precise control of attention and its involvement stimulation, here we show that covert attention flexibly improves and speeds up both detection and at discrimination loci only a foveola, the small yet important rod-free disproportionally region of the retina. Using new methods for precisely controlling retinal however, whether selective spatial attention operates where the observer is already looking—that is, within the high-acuity known to covertly enhance processing at locations away from the center of gaze, where visual resolution is low. It is unknown, Efficient control of attentional resources and high-acuity vision are both fundamental for survival. Shifts in visual attention are Poletti Martina Selective attention within the foveola NATURE NATURE Received 22 November 2016; accepted 9 July 2017; published online 14 August 2017; Department of Psychological & Brain Sciences, Boston, University, Boston, Massachusetts, USA. Until recently, rendered it difficulties technical impossible to inves At first sight, it may appear that studying covert attention in the the in attention covert studying that appear may it sight, first At NEUR OSCI 1– 4 , and alters the signal at the target location during during location target the at signal the alters and , 3 1 Department of Psychology, New York University, New York, New York, USA. EN 5–

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3 , 4 previous studies. We then investigated the consequences of attention We studies. consequences the previous investigated then (ref. (ref. deg 1 about is that uncertainty of area an yield typically methods These video-oculography. of standard limits the is beyond that ment require a fixation, of locus retinal preferred the to respect with ulus ( field? visual the of portion tiny this in tions loca at specific vision enhance to selectively fine-tuned be attention Can foveola? the within is, that gaze; of center at the already ery, but What happens when the is attended location not in periph the visual Foveal control of attention facilitates detection performance extrafoveal by improving effects these attenuate effectively can attention and eccentricity, ing vision because various visual functions gradually decline with increas for extrafoveal beneficial is highly enhancement Such of gaze. center away from the many degrees were presented stimuli in which studies ANOVA high with times (in shorter reaction it fact, increased; slightly remained as accuracy trade-offs, of speed–accuracy the consequence location ( unattended the detection—at cost—slower a and location the attended detection—at benefit—faster a in resulted attention condition, neutral the to compared expected, As attention. covert (voluntary) ( foveal stimuli para with task cueingspatial central a consistedof 1 Experiment RESULTS foveola. the within tasks 4) and 3 (experiments discrimination and 2) (experiment detection both for jection of the attended location across the foveolatheattended acrosslocationthe of jection movements eye fixational incessant from resulting motion retinal the with dealing requires it Fig. Fig. 2 Studying attentional control within the foveola is challenging challenging is foveola the within control attentional Studying doi:10.1038/nn.462 2 2 a ), approximately the size of the entire foveola. Furthermore, Furthermore, foveola. entire the of size the approximately ), ). It requires high accuracy in localizing the position of a stim F Fig. Fig. 1 (2,4) = 14.9; 14.9; = (2,4) 4 2 Center Center for Neural Science, New York University, New York, New Graduate Graduate Program in Boston Neuroscience, University, Boston, Fig. Fig. 1a c , ANOVA 2 , b P ), a standard procedure to study endogenous to endogenous study procedure ), a standard = 0.002), and it is consistent with previous previous with consistent is it and 0.002), = 1 F 3 (2,4) = 23.6; , which continually shift the retinal pro retinal the shift continually which , 1– P 4 = 0.0004). This is effect not . ART 23 , 2 4 ( Fig. 2b Fig. IC Fig. Fig. 1 LE , d d S ). ). 1 2 ------,

© 2017 Nature America, Inc., part of Springer Nature. All rights reserved. apart ( apart (0.33°) arcmin 20 only now were locations unattended and attended the stimuli of used in experimentthose 1 (ref.matched approximately representations cortical their that so size in down scaled were stimuli the experiment, this In degree). a of 1/60 = arcmin (1 gaze of center the from away arcminutes few in shown one the to similar task cueing spatial a in performance tested ( movements eye fixational of presence continual the despite eccentricities foveal tion methods standard to compared nitude mag of order one than more by fixation of locus retinal preferred the of center the of localization improves effectively that procedure calibration gaze-contingent a (i) of use tempo enabled and This resolution. spatial ral high with device a eyetracker, Image Purkinje control display gaze-contingent for system field. visual the of portion high-resolution the within attention where resolution is visual lower, cannot they be gaze, applied to selective examine of center the from far presented are stimuli when well work attention covert study to procedures standard whereas Thus, without blinks, saccades, and/or microsaccades (see Online Methods). trials on based are study this in reported analyses all stimulation, visual Tocolor. optimal ensure a different by marked each observers, individual P P P (Tukey HSD (neutral trials). Error bars are 95% confidence interval (CI). * value predictive no had and trials), (invalid location wrong the predicted trials), (valid location target the predicted correctly cue the which in expressed as index of sensitivity ( ( acuity. visual highest of region the foveola, the from away attention shift covertly to need observers that so eccentricity), 3° (at gaze of voluntary attention. ( deployment the ensures onsets target and cue between delay The validity). cue (76% location likely most its indicating target, the precedes always cue A central possible. as accurately and quickly as squares) empty (black locations two of one at square) (red a target of appearance the report cueing task. Observers ( Figure 1 ART 2 faster at targets detecting presented at the attended location (ANOVA c b 500 ms a Time

= 0.0041; neutral vs. invalid invalid vs. neutral 0.0041; = neutral, vs. valid Sensitivity: 0.0105. = invalid, vs. valid 0.0476; = ) Average reaction times for correct responses and ( All observers exhibited the classical attention effects, even though though even effects, attention classical the exhibited observers All state-of-the-art a on relied we limitations, these circumvent To Figure Figure 400–700 ms 100 ms 2 0 to ensure that visual stimuli always remained at the desired desired the at remained always stimuli visual that ensure to Fig. 2 Fig. Fixation marker

IC Attention control in the parafovea (experiment 1). ( 100 ms 1 Cu post hoc , but for targets appearing well within the foveola, only a only foveola, the within well appearing targets for but , LE e e Fig. 2 Fig. ). As with stimuli outside the foveola, observers were were observers foveola, the outside stimuli with As ). S tests. Reaction times: valid trials vs. neutral trials, trials, neutral vs. trials valid times: Reaction tests. c Target ). Using these techniques, in experiment 2 we we 2 experiment in techniques, these Using ). b n ) Targets are presented far from the center of center the from far ) Targetspresented are = 5) maintain fixation on a central marker and and marker a central on fixation maintain = 5) P = 0.0003; neutral vs. invalid, invalid, vs. neutral = 0.0003; P c = 0.9878). Dots represent data from from data represent Dots = 0.9878). d Reaction time (ms) ` 17 21 25 ) in the three types of trials: those those trials: of types three the ) in 0 0 0 Foveola Valid 2 P 20

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- - - visual field. the of rest the in as just foveola, the in ones unattended of expense the at locations attended at detection facilitates attention that show those to measured in experimentidentical 1 ( virtually were characteristics movement eye bilization, ANOVA ( trials valid the in increased slightly even it and conditions, all in high remained accuracy accuracy; of cost the at come not did times reaction faster is, that present: was trade-off speed–accuracy no Again, smaller. 20 times now was approximately locations tended paired ment ms 22 (foveola: 1 experi in measured one the to similar was trials invalid and valid in times reaction between difference The distance. retinal with change F P neutral, invalid, tests. Reaction times: valid trials vs. neutral trials, S5: tests; S1: sum rank Wilcoxon (two-tailed (S1–S5) 1–5 subjects observers, individual all for significant statistically were trials invalid and valid between times for different trial types across observers ( during the course of a trial. ( observer’s eye movements (black arrow). ( the for compensate to arrows), (cyan control computer under time, real in ( itself. foveola the as large as area an by mosaic photoreceptor the over image retinal the displace normally which movements, eye nearby locations. ( at stimuli of presentation precise requires foveola the in task cueing Figure 2 c d = 0.9992). Conventions are as in in as are Conventions 0.9992). = b (2,4) = 25.5; = (2,4) a ) Stimuli were maintained at the desired eccentricities by moving them them moving by eccentricities desired the at maintained were ) Stimuli Gaze position (arcmin) P −4 4 0 = 0.0009). Error bars are 95% CI. * CI. 95% are bars Error 0.0009). = Microsaccades Ocular drift t P

P -test, = 0.0003; neutral vs. invalid, invalid, vs. neutral 0.0003; = Attention control within the foveola (experiment 2). ( = 0.0135; valid vs. invalid, invalid, vs. valid 0.0135; = F P ADVANCE ONLINE PUBLICATION Target Cue (2,4) = 9.6; = (2,4) = 0.004; S2: S2: 0.004; = 500 Time (ms) P Normal viewing = 0.31), but the distance between attended and unat and attended between distance the but 0.31), = P 1,000 = 0.0003). Notably, the effect of attention did not not did attention of effect the Notably, 0.0003). = b ) This requirement is challenged by incessant small small incessant by challenged is requirement ) This y x 10 arcmin 1,500 P o = 0.008). Also note that despite retinal sta retinal despite that note Also 0.008). = P 5 ms; parafovea: 25 ms ms 25 parafovea: ms; 5 = 0.022; S3: S3: 0.022; = e ) Average reaction times and ( Reaction time (ms) e 300 220 260 Figure Supplementary Fig. 1 Supplementary

Valid c P = 0.0128; neutral vs. invalid invalid vs. neutral = 0.0128; P n Neutral Display (enlarged) d = 0.0472. Sensitivity: valid vs. vs. valid Sensitivity: = 0.0472. P = 5). Differences in reaction reaction in Differences = 5). * P Retinal stabilization 1 ) An example of eye movements movements eye of example ) An = 0.039; S4: S4: 0.039; = < 0.05 (Tukey HSD HSD (Tukey 0.05 < . *

Invalid * NATURE NATURE 5 arcmin(0.08 10 arcmin(0.1 Foveola P = 0.0074; valid vs. vs. valid = 0.0074; 1 o 10 ms; two-tailed two-tailed ms; 10 Sensitivity (d) f NEUR Retina (enlarged) 5 3 4 P = 0.0009; = 0.0009; f Valid ) accuracy ) accuracy ° ). These data ). These 6 ) ° a

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f E - - - , © 2017 Nature America, Inc., part of Springer Nature. All rights reserved. in experiment 3. Observers were asked to report the orientation of a of orientation the report to asked were Observers 3. experiment in task discrimination cueing spatial a used we hypothesis, this tigate To vision. inves role in high-acuity may play an attention important foveola in detection (experiment 2) suggests that microscopic shifts of of the and tion of control within the attentional patterns, finding fine is a question given that critical many require examina daily activities stimuli. Can attention also enhance discrimination of fine detail? This The data in discrimination spatial fine enhances attention of control Foveal and foveola. the outside inside way similar a in detection facilitates attention ferences, represented is space foveal where colliculus, regions two the in neurons magnocellular and parvocellular of proportions cone of characteristics photoreceptors in the fovea and the in the periphery visual as such factors, various from originate than by pressing rather a button location ( its toward microsaccade a performing by target the were to asked report observers when results In we found similar fact, stimulus eccentric more a toward saccade larger a than fovea the within already stimulus a toward microsaccade a generate to longer stimuli. parafoveal and foveal of processing the in differences qualitative at point perifovea—and for information accrual stimuli presented in the parafovea than in the fovea the outside reported effects dependent 46 was time reaction paired ( experiments both in able compare the foveola than in the parafovea ( (76% cue validity). ( location likely most its indicated that cue a central by preceded was target The horizontally. or vertically tilted was marker, fixation the from away arcmin Figure 3 NATURE NATURE valid vs. neutral, post hoc trials in which the cue and the target were presented in the same and opposite hemifield, respectively. Error bars are 95% CI. * P P Differences between valid and invalid trials were statistically significant for all individuals (sensitivity, two-tailed a 10 × 6.4 = S3: 0.01; = Oculomotor reaction times also follow a similar trend: it takes takes it trend: similar a follow also times reaction Oculomotor Of note, wereobservers slower at detecting targets presented within 500 ms Possible targetlocations Tim t 100 ms 30 14 arcmin

-tests). On average, across all types of trials, the increment in increment the of trials, types all across On average, -tests). tests. Sensitivity: valid trials vs. neutral trials, trials, neutral vs. trials valid Sensitivity: tests. e NEUR Attention and fine spatial discrimination (experiment 3). ( Figs. 1c , 3 1 , and/or influences from the rostral part of the superior superior the of part rostral the from influences and/or , Figure Figure −16 P 600 ms OSCI 10 × 4.9 = ; S3: P and = 0.0009; valid vs. invalid, invalid, vs. valid 0.0009; = 100 ms 2 b EN P , show that attention upspeeds of detection foveal 2 c o Fixation marker 10 × 2.1 = ) Experimental results, measured as ( C e 3 ms. These findings parallel the eccentricity- the parallel 3 findings ms. These ), even though the stimuli were equally detect E

−4 Supplementary Fig. 2 P ADVANCE ONLINE PUBLICATION ; S4: > 0.77 in all three trial types, two-tailed two-tailed types, trial three all in 0.77 > Cue −10 P P < = 0.019; S5: S5: 0.019; = ; S4: Target 0.0001, two-tailed paired paired two-tailed 0.0001, P 10 × 1.7 = P 3 = 0.00004; neutral vs. invalid invalid vs. neutral 0.00004; = 2 2 . . Yet,dif these despite b 7 P —namely, the slower slower the —namely, ). These effects might Sensitivity (d) 10 × 2.9 = 1 2 3 P −11 = 0.0123; valid vs. invalid, invalid, vs. valid 0.0123; = 2 Valid 9 ; S5: , , the different b ) accuracy (

−12 * P Neutral 10 × 8 = . Reaction times, two-tailed Wilcoxon rank sum tests: S1: a * t ) Observers reported whether a tiny bar, which could appear in one of four boxes 14 boxes four of one in appear could bar, which a tiny whether reported ) Observers -test; -test; * 2 8 - - - - Invalid . d ` ) and ( −24 continues to operate in the presence of the physiological motion of of motion physiological the of presence the in operate to continues min; ANOVA marker from distance example, (for marker fixation the to < P ANOVAarcmin; 14 > target from distance example, localizationtionprocedure high-resolu our of means by gaze—determined of center the which ( microsaccades locus retinal preferred a on stimulus the of repositioning movements eye consequence fixational the not were enhancements perceptual bilization, sta retinal under As location. unattended the at discrimination— and and at a slower location, cost—lower the attended crimination— dis faster and benefit—higher a in resulted attention condition, (ANOVA (ANOVAcantaccuracy fixation(experiment 4, ( 3 experiment of hemifield. same the within arcmin 20 by only shifts retained a high degree of even selectivity for locations separated ( target the as hemifield opposite or same the within fell location this whether of irrespective similar, was location ‘wrong’ at the attention focusing from resulting cost the Moreover, trials. neutral the to tive costs occurred, respectively, in the valid- and invalid-cue relatrials and benefits significant times, reaction and accuracy both for Thus, fasteralso validintrials(ANOVA trials ( invalid and neutral the in than location, correctly target cue the the predicted when trials, valid the in higher significantly was ( foveola the within eccentricity same the at all locations, possible four at appear could that bar tiny Fig. 3b Fig. Fig. 3 Fig. ). Accuracy and reaction times are also shown separately for the invalid invalid the for separately shown also are times reaction and Accuracy ). P We also obtained similar results when the discrimination task task discrimination the when results similar obtained also We sensitivity of index the as expressed accuracy, Discrimination = 0.0084). Conventions are as in in as are Conventions 0.0084). = 0.0001) and in trials in which the center of gaze remained close close remained gaze of center the which in trials in and 0.0001) c ) reaction times, for different trial types across observers ( Opp. b P Opposite hemifeld hemifeld , ; ANOVA; = 0.00004; neutral vs. invalid, invalid, vs. neutral 0.00004; = Same c , F P (2,4) = 98; = (2,4) = 0.83 two-tailed paired 2 Same 0 F . These effects were also present in the trials without without trials the in present also were effects These . (2,4) = 19; Supplementary Fig. 3 Fig. Supplementary Fig. Fig. F (2,4) = 49.9; = (2,4) c P < P 3 Reaction time (ms) ) was repeated with normal, nonstabilized, nonstabilized, normal, with repeated was ) Fig. Fig. F 500 600 700 800 900 (2,4) = 79; = (2,4) 0.0001) effects. Compared to the neutral neutral the to Compared effects. 0.0001) P = 20 4 , 0.0009). Thus, fine attentional control control attentional fine Thus, 0.0009). 2 ). In this case also, there were signifi were there also, case this In ). 5 —remained far from the target (for (for target the from far —remained Fig. 3 Fig. z Valid -tests: S1: P < P Figure F (2,4) = 51; = (2,4) * P < P 0.0001). Reaction times were were times Reaction 0.0001). a P Neutral t ). = 0.0008. Reaction times: times: Reaction = 0.0008. ), as well as both in trials in in trials in both as well as ), -test). Therefore, attentional attentional Therefore, -test). * 0.0001) and reaction time time reaction and 0.0001) 1 . P P * 10 × 1.9 = 10 × 1.6 = P Invalid < 0.05 (Tukey < 0.05 HSD P < P ART 0.0001, −7 −9 F Opp. ; S2: ; S2: (2,4) = 52; 52; = (2,4) ; S2: ; S2: IC n = 5). = 5). Fig. 3 Fig. < 7 arc LE

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© 2017 Nature America, Inc., part of Springer Nature. All rights reserved. previous findings on the contributions of very small eye movements movements eye small very of contributions the on findings previous crowded visual stimuli attention may also help alleviate the processing challenges posed by the enhancing selected foveal subregions, as occurs extrafoveally locations retinal nearby at similar ance a serve may deployment balancing function within the attentional foveola, by tempering that uneven perform suggest results functionallevels the and fovea the between periphery function visual in gaps attention attenuate covert to of is function looking. important an already that is argued been observer has It the where locations selected at at vision ance low-resolution enhancing for improvingforhigh-acuityperipheral performlocations,also but useful only not are tion of atten shifts Covert vision. pattern fine to contribute mechanisms gaze. of center very at the precision surprising with controlled be can it and field, visual the throughout information modulates that mechanism selection a as acts attention Covert misleading. is fovea the from far only operates that process a as attention covert of view intuitive the that reveal findings These stimulus. of the observed of and demands the task the characteristics to the according varies acuity, but allocation its of highest region the tion assump widespread to contrary is, That gaze. of center the at arc of minutes few a by only separated locations across shifted and regions selective enhancement of visual processing can be restricted to narrow assumed: hitherto than flexible and fine-grained more much is tion ( 3 and 2 experiments of results The DISCUSSION ( instability fixational natural of because foveola the across move stimuli when image, retinal the P P neutral vs. invalid, trials vs. neutral trials, bars are 95% CI. * ( because of the physiological instability of fixation. ( 3 ( experiment to identical experiment a control of Results 4). (experiment Figure 4 ART 4 b

= 0.0001). Conventions are as in in as are Conventions 0.0001). = invalid, vs. valid 0.0010; = a ) reaction times for different trial types across observers ( A direct consequence of our findings is that covert attentional attentional covert that is findings our of consequence direct A Fig. Sensitivity (d) 1– 1 2 3 4 3 , 8

IC ), but without retinal stabilization. Stimuli moved on the retina retina the on moved Stimuli stabilization. retinal without but ), , Fine attentional control during normal retinal image motion motion image retinal normal during control attentional Fine 15 1 Valid , , 3 4 3 LE Lc o hmgniy t oh h anatomical the both at homogeneity of Lack . , spatial attention is not uniformly distributed within within distributed uniformly not is attention spatial , * S 2 Neutral P P 0 < 0.05 (Tukey HSD HSD (Tukey 0.05 < has also been reported in the foveola. Thus, our our Thus, foveola. the in reported been also has = 0.0004. Reaction times: valid vs. neutral, neutral, vs. valid times: Reaction = 0.0004. * P 3 = 0.0010; valid vs. invalid, invalid, vs. valid 0.0010; = 5 * typical of natural scenes. In sum, together with Invalid P = 0.00004; neutral vs. invalid invalid vs. neutral = 0.00004; Supplementary Fig. 4b Fig. Supplementary 2 0 Figure . Furthermore, by prioritizing and and prioritizing by Furthermore, . b

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sized by our finding that observers retained attentional specificity specificity ( attentional retained observers that finding our by sized empha is process such for need The saccades. between intervals the in even necessary is locations foveal attended the of registration the eyes move by amounts that are relevant at this scale this relevantat areamounts that by move eyes the with area eccentricity decreasing cortical dedicated the expands which magnification, cal corti to thanks resolution required the reach may responses, neural synchronization the toward fields the location attended receptive neuronal com of convergence the a as such that mechanisms, attentional is postulated monly possibility One eccentricities. farther at attention of control coarse the for responsible held mechanisms neural the to attributed that than generally specificity spatial much higher possess (iii) and instability, fixational during representations these updating for continually mechanisms include (ii) of region field, tral the visual dedicated high-resolution representations (saliency maps) of the cen responsible for controlling attention. These processes must (i) include role. critical a plays attention covert of outcome of a complex visuomotorthe as interaction but in which precise accomplishment, control sensory purely a as regarded be cannot tasks high-acuity to t the in available are references, and codes accession statements of including Methods, and data availability any associated M of acuity. highest region the including field, visual the throughout processing ing accelerat and improving selectively more for evolved a mechanism of general manifestation the is but looks, observer the where from attention is not a process that facilitates perceptual computations away call for a generalization of the very concept of covert attention. Covert at of field center the of gaze visual the portion high-acuity the within events. oculomotor these of absence the in even present are parafovea the and foveola the in locations— unattended the at costs and location attended the at offs—benefits trade attentional microsaccades: to tied necessarily not are shifts effects attention mediate to vision tern pat fine enhance further to locus foveal preferred the on interest of stimulus the center would then which by out microsaccades, carried tion to similar here those reported could also precede overt responses enforced not is fixation when features task-relevant on sight of line the center precisely microsaccades that observed recently been has It maintained fixation. during fovea the inside, not but outside, far measured however, have been modulations, These foveola. the within stimulus microsaccades of presence the in saccade the at vision target locations enhance and saccades of execution the cede positions retinal in movements. eye by fixational changes caused for account to needs it as resolution, periphery visual the in saccades during studied to those similar qualitatively updating of spatial mechanisms ( locations tended unat and attended between separation the to comparable distances he he pape Supplementary Fig. 3 Fig. Supplementary ET Our results have several implications for the neuronal processes processes neuronal the for implications several have results Our To conclude, our finding that shifts in covert attention occur even even occur attention covert in shifts that To finding our conclude, pre to attentionknownare ofexploration, shiftsvisual During H ODS r 2 . 5 ADVANCE ONLINE PUBLICATION . We therefore hypothesize that microscopic shifts in atten 2 0 . Critically, although microsaccades have been claimed claimed been have microsaccades although Critically, . 5– 7 . Attentional modulations have also been observed . have observed Attentional been also modulations Supplementary Fig. 4b Fig. Supplementary 14 3 8 , and/or the general correlated structure correlated general the and/or 3 6 ) even though their eye movements covered covered movements eye their though even ) 26 , our results indicate that fine spatial vision vision spatial fine that indicate results our , , 4 1 4 . However, given that, during fixation, fixation, during that, given However, . 5 , our results show that covert attention attention covert that show results our , 4 4 , small saccades that keep the the keep that saccades small , 7 , 11

). This capability calls for for calls capability This ). , 4 NATURE NATURE 3 , but with much higher higher much with but , online version of version online NEUR 4 , 3 7 , , changes in OSCI 4 2 , spatial spatial , 39 EN , 4 0 of C E ------

© 2017 Nature America, Inc., part of Springer Nature. All rights reserved. 17. 16. 15. 14. 13. 12. 11. 10. 9. 8. 7. 6. 5. 4. 3. 2. 1. jurisdictional claims in published maps and institutional affiliations. reprints/index.htm at online available is information permissions and Reprints The authors declare no competing financial interests. data, and the writing of the manuscript. contributed to the design of the experiments, the interpretation of experimental M.P. conceived the study and and collected analyzed the data. The three authors collection. data with for helping Ezzo R. and S. Ling, E. Niebur, M. Spering, J. Victor, A. White and Y. Yeshurun for comments R01-EY019693 (M.C) (M.R.), and R01-EY016200 (M.C). We thank M. Landy, (M.P.) and and1420212 (M.R.), National Institutes of Health grants R01-EY18363 This work was supported by National FoundationScience grants BCS-1534932 version of the pape the in available are files Data Source and Information Supplementary Any Note: NATURE NATURE COM AU ACKNOWLEDGMENT

T Nakayama, K. & Mackeben, M. Sustained and transient components of focal visual focal of components transient and Sustained M. Mackeben, & K. Nakayama, of characteristics spatial focal and of field the around and within attention Visual J.D. C.W.James, Eriksen, St & Temporal J.E. Hoffman, & C.W. Eriksen, movements. eye fixational of functions and Control M. Poletti, & M. Rucci, years. 25 past the movements: Eye microsaccades: of E. study Kowler, the to guide field compact A M. Rucci, & M. Poletti, remapping on based stability Visual M. Rolfs, P.,& Cavanagh, A. Afraz, A.R., Hunt, photoreceptor Human A.E. Hendrickson, & R.E. Kalina, K.R., spatial Sloan, C.A., Curcio, visual and colliculus Superior A. Zénon, & L.P. Lovejoy, R.J., Krauzlis, course. time and representation, control, attention: Visual Yantis,S. & H.E. Egeth, tuning. sensory reshapes preparation Saccade M. Carrasco, & A. Barbot, H.H., Li, the in attention Schall, J.D. On of the role of frontal eye field in guiding attention and saccades. role The E. Blaser, & B. Dosher, E., Anderson, E., Kowler, resolution: spatial of enhancement Attentional M. Carrasco, & K. Anton-Erxleben, Psychophysical, sensitivity: contrast increases attention Covert M. Carrasco, processing. visual of modulation Attentional L. Chelazzi, & J.H. Reynolds, years. 25 past the attention: Visual M. Carrasco, attention. model. lens zoom a attention: (1972). displays. visual from encoding selective Sci. Vis. Rev. (2011). functions. and challenges pointers. attention of topography. attention. Psychol. Rev. Annu. Biol. Curr. Res. saccades. of programming evidence. (2013). 188–200 neurophysiological and behavioural linking (2006). erpyilgcl n nuomgn studies. neuroimaging and neurophysiological Neurosci. Rev. (2011). H P O ET

44 R NEUR I CONT , 1453–1467 (2004). 1453–1467 , NG

Vision Res. Vision Neurosci. Rev. Annu. 26 FI J. Comp. Neurol. Comp. J.

, 1564–1570 (2016). 1564–1570 , OSCI 1

r N l RIBU 27 . . Publisher’s with neutral Nature remains regard to note: Springer , 499–518 (2015). 499–518 , . A , 611–647 (2004). 611–647 , NC

EN 48

T Trends Cogn. Sci. TrendsCogn. IA 29 S I , 269–297 (1997). 269–297 , C ON L , 1631–1647 (1989). 1631–1647 , E I Vision Res. Vision Vision Res. Vision

NTE S

ADVANCE ONLINE PUBLICATION 292 Percept. Psychophys. Percept.

36 R , 497–523 (1990). 497–523 , E , 165–182 (2013). 165–182 , S

118 35

S 14 Percept. Psychophys. Percept. , 1897–1916 (1995). 1897–1916 , , 83–97 (2016). 83–97 , , 147–153 (2010). 147–153 , rg Ban Res. Brain Prog.

iin Res. Vision iin Res. Vision 40 , 225–240 (1986). 225–240 , a. e. Neurosci. Rev. Nat. http://www.nature

51 51 , 2-B, 201–204 2-B, ,

1457–1483 , 1484–1525 , 154

33–70 , online Vision .com/ Annu. Annu.

14 ,

32. 31. 30. 29. 28. 27. 26. 25. 24. 23. 22. 21. 20. 19. 18. 45. 44. 43. 42. 41. 40. 39. 38. 37. 36. 35. 34. 33.

ofr, . Hfd ZM & ruls RJ Vsa fiain s qiiru: evidence equilibrium: as fixation Visual R.J. Krauzlis, & Z.M. Hafed, L., Goffart, the of organization retinotopic and Laminar F.H. Baker, & D. Lee, J.G., Malpeli, and magnocellular of mapping Uneven A. Cowey, & K.E. Jones, P., Azzopardi, R. Sinha, saccades. small of characteristics Latency R.M. Steinman, & D. Wyman, cortical the and Carrasco, M., McElree, B., Denisova, sensitivity,K. & Giordano, A.M. Speed of visual contrast processing resolution, Visual J. Rovamo, & V. Virsu, high a in gaze relocate precisely Microsaccades M. Rucci, & M. Poletti, H.-K., Ko, natural during retina the to input visual The M. Rucci, & J.D. Victor, M., Aytekin, scale. microscopic a at coordination Head-eye M. Rucci, & M. Aytekin, M., Poletti, Holmqvist, K. system general-purpose a EyeRIS: M. Rucci, & R. Iovin, G., Redner, F., Santini, for compensate movements eye Microscopic M. Rucci, & C. Listorti, M., Poletti, task to according resolution spatial modifies Attention M. Carrasco, & A. Barbot, attention. visual of resolution spatial The P. Cavanagh, & J. Intriligator, ae, .. leain f iul ecpin ro t microsaccades. to prior perception visual of Alteration Z.M. Hafed, microsaccades Spontaneous D.J. Heeger, & E.P. Merriam, S., Yuval-Greenberg, eye across attention of constancy Spatial M. Zorzi, & P. Cavanagh, M., Lisi, in fixation sustained of Precision M. Rucci, & M. Poletti, X., Kuang, C., Cherici, primary the in fovea the of representation Preferential A. Cowey, decorrelates & P. Azzopardi, attention Spatial J.H. Reynolds, & K.A. Sundberg, by J.F., primarily Mitchell, performance improves Attention J.H.R. Maunsell, & M.R. Cohen, oscillatory of Modulation R. Desimone, & A.E. Rorie, J.H., Reynolds, P., Fries, shrinkage and shift field Receptive Treue,S. & K. T.,Womelsdorf,Anton-Erxleben, enhance movements eye Miniature F. Santini, & M. Poletti, R., Iovin, M., Rucci, cortical and crowding acuity, Vernier A.P. Aitsebaomo, & S.A. Klein, D.M., Levi, diminishes location target the to attention Precueing E. Rashal, & Y. Yeshurun, resolution. Attentional J. Intriligator, P.& Cavanagh, S., He, functions. magnification parvocellular and magnocellular nucleus: geniculate lateral macaque monkey. macaque the in cortex striate the to nucleus geniculate lateral the from projections parvocellular fovea. primate the of Res. eccentricity. with increases factor. magnification task. acuity visual fixation. head-free Biol. Curr. 2011). Press, Univ. (Oxford 775–786 (2013). 775–786 attention. covert in shifts reflect objects. visual of presence the by Psychophys. mediated is movements observers. untrained and trained cortex. visual V4. area macaque in fluctuations activity intrinsic correlations. interneuronal reducing (2001). attention. visual selective by synchronization neuronal 28 modulation. gain attentional through area temporal middle macaque in detail. spatial fine magnification. distance. critical the reduces and crowding (1997). 115–121 inactivation. colliculus superior from (2007). control. display eye-movement-contingent for fovea. the within vision nonhomogeneous demands. Psychol. , 8934–8944 (2008). 8934–8944 ,

13 , 2173–2175 (1973). 2173–2175 ,

43 et al. et

Psychol. Sci. Psychol. J. Comp. Neurol. Comp. J. 25 , 171–216 (2001). 171–216 ,

77 , 3253–3259 (2015). 3253–3259 , Nature et al. Vision Res. Vision Cellular and circuit mechanisms shaping the perceptual properties perceptual the shaping mechanisms circuit and Cellular , 1159–1169 (2015). 1159–1169 , J. Neurosci. J. Nat. Neurosci. Nat.

Nature Eye Tracking: A Comprehensive Guide to Methods and Measures

Exp. Brain Res. Brain Exp. 361 Cell Vision Res. Vision

28 , 719–721 (1993). 719–721 ,

447 168 25 , 285–296 (2017). 285–296 ,

Nat. Neurosci. Nat. 375 , 963–977 (1985). 963–977 , , 851–854 (2007). 851–854 , , 413–426 (2017). 413–426 ,

34 , 363–377 (1996). 363–377 , J. Neurosci. J.

J. Vis. J.

13 , 12701–12715 (2014). 12701–12715 , 39 Nat. Neurosci. Nat.

, 1549–1553 (2010). 1549–1553 , J. Neurosci. J. , 2179–2189 (1999). 2179–2189 , 37

12 , 475–494 (1979). 475–494 , Curr. Biol. Curr.

, 1–16 (2012). 1–16 , 6 J. Vis. J. , 699–700 (2003). 699–700 ,

34 ea. e. Methods Res. Behav. , 13693–13700 (2014). 13693–13700 ,

Neuron 10 12

, 10627–10636 (2012). 10627–10636 , 23 , 16 (2010). 16 , , 1594–1600 (2009). 1594–1600 , Science , 1691–1695 (2013). 1691–1695 ,

63 ART Trends Cogn. Sci. Cogn. Trends , 879–888 (2009). 879–888 ,

291 te. Percept. Atten.

39 1560–1563 , IC Neuron J. Neurosci. J. 350–364 , LE Cognit. Vision

S 1 5 , ,

© 2017 Nature America, Inc., part of Springer Nature. All rights reserved. the targetthe were displayed forinter-stimulusanms,with100 randomlyinterval direction (invalid trials), or in both directions (neutral trials). Both the cue and center of the display) that pointed toward the target (valid trials), in the opposite point of fixation and, in all trials, was preceded by a cue (a horizontal bar at the appeared at one of two possible locations, either to the left or to the right of the square)redtarget (astandardThe task.detection ausing cueingspatial lected cone density highest of locus foveal the with coincide necessarily not does and fixation of preferred locus retinalcorrespondsthe way to this estimated in gaze center of as microscopic head movements that may occur even on a bite bar. Note that the tion before each trial to compensate for possible drifts in the electronics as well necessary. The manual calibration procedure was repeated for the central posi locationpredictedif gazefine-tunethe tojoypad a used Observers screen. the on time real in displayedautomatic was calibrationthe of basis the on mated on each of the nine points of the grid while the location of the line of sight esti again fixating automaticbycalibration the byvoltage-to-pixel mappinggiven the refined or confirmed calibration),observers (manual phase second the In were located 1.32° apart from each other on both the horizontal and pointsvertical of a 3 axes.× 3 grid, as it is standard in oculomotor experiments. These points phase (automatic calibration), observers sequentially fixated on each of the nine by approximately one order of magnitude over standard methods fixation of locus preferredretinal gaze- the procedureimprovesof Thislocalization two-step a executing and contingent performance, calibration procedure to optimal map the eyetracker’s for output to eyetracker visual angles. the apparatus,the tuning in observer involvedcomfortablythewhich positioning minutes, few a lasted that operations setup preliminary with started session Every sessions. lasted 12 average on completed session subject each and Each h, approximately day.1 the of times various at sessions experimental tiple tasks. experimental and Procedure (two frames) were discarded (less than 10 trials per observer). by EyeRIS during the experiments. All trials in which the delay exceeded 14 ms the recorded oculomotor traces to the coordinates of the stabilizedlization errorstimulus of approximatelysaved 1 arcmin, as measured a posteriori by comparing (the time required to render 1.5 frames on the display), which resulted in a stabi estimated center of gaze. The delay of the system in these experiments was 10 ms both the cue and target remained at fixed foveal eccentricities with respect to the EyeRIS control, to compensate for the observer’s eye movements, ensuring that achieved by means of retinal stabilization. The stimulus movedcombination of estimatedin oculomotor variables.real Precise foveal stimulationtime, was under desired the to accordingdisplay the on stimulus the updates and time real in This system acquires eye movement signals from the eyetracker, processes them gaze-contingentcontrol.displayflexible allows hardware, dedicatedwhich on analysis. for at subsequent 1 were sampled and kHz recorded and of a resolution 1 spatial arcmin (ref. tracker (Fourward Technologies), a system with an internal noise of ~20 arcsec eye were measured by means of a Generation 6 Dual Purkinje Image (DPI) eye bite bar and a headrest prevented head movements. The movements of the right monocularly with their right eye while the left eye was patched. A dental-imprint150 Hz and spatial resolution of 768 × 1,024 of pixels.rate refresh vertical Observersa at performedHM204DT)(Iyama monitorCRTfast-phosphor a the task apparatus. control gaze-contingent and Stimuli River Campus Institutional Review Board. all participants following procedures approved by the Boston University Charles stabilization of the stimulus on the retina. Informed consent was obtained from ments. Only emmetropic observers were enrolled in this study to ensure optimal 4 ( in experiment and 3 females) ( 3 experiment in females) 3 and males (2 in experiment the in part took subjects these of ers (2 males and 3 females) took part in experiments 1 and 2 ( pose of the study, participated in the experiments (age range 20–29). O Five observ ONLINE MET NATURE NATURE alternating between 400 and 700 ms. Observers were instructed to press one of bservers. Detection experiments. of by EyeRIS means rendered were Stimuli NEUR A total of thirteen emmetropic human observers, all naive to the pur the to naive all observers, human emmetropic thirteen of total A 47 , 4 8 OSCI . H ODS EN Data in experiments 1 and 2 ( 2 and 1 experiments in Data C E Fig. Fig. 4 Data were collected by means of mul ). One observer participated in all experi 4 6 ). Vertical and horizontal eye positions Fig. Fig. 2 1 , a custom-developed system based 3 Supplementary Figure 2 Figure Supplementary ), and five observers (2 males (2 observers five and ), Stimuli were displayed on displayed were Stimuli Figs. 1 1 Figs. Figs. Figs. 1 and 1 2

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differentrandomized.was types underAlthoughtrials fading visualoccur can thecenter of thedisplay throughout thecourse of and thetrial, presentation of movements. eye fixational of their fixed locations at the center of the display and moved on the retina because ( 30% of all trials). target location; 17% of all trials) or neutral (a cue pointed in all four directions; of all trials and 76% of directional trials), invalid (incongruent cue direction and of trials were presented: valid (congruent cue direction and target location; 53% from the fixation point. A central cue preceded the target by 600 ms. Three types boxes (7 arcmin × 7 arcmin) surrounding a central fixation point, eachbypressing one 14of two keys on the joypad. arcminThe bar could appear in one of four horizontallyorarcmin)verticallytiltedarcmin 2 was (7 × bar small a whether appeared at only 10 arcmin eccentricity, well within the foveola. from the center of gaze. In experiment 2 ( presentedarcminwastargetsize)arcminparafovea, 10 (10inthe × in away 3° evaluated over 194 trials per trial type per observer. with microsaccades were included in the analyses. On average, performance was when less conservative selection criteria were applied—for example, when trials numberavailableonthe ages, of trials based participant, per wereand/or used trials varied slightly across observers. Results did not change when weighted aver fixational eye movements, the proportion of selected valid, invalid, and neutral different experiments. However, because of well-known individual variability in movements did not differ in these two experiments. experimentstwothe ( also applied in experiment 1 to enable rigorous comparison between data from excluded observer,trials 10 per sameThecriteriatotalof trials). were~1%the ms and >1,000 in detection; responding( anticipationin delays ortheir by revealed as task, the in the total trials). We also discarded trials in which the observers were not engagedtrajectory—exceeded 0.5° during the period between cue and target onset (7% of the ocular span—defined as the radius of the smallest circle encompassing150 ms beforethe eye cue presentation (overall, 25% of the totalcades attrials), any andpoint trials during in thewhich trial, trials with microsaccades at fast anyfor the stabilizationtime apparatus.later These thanincluded trials with blinks and/or sac all trials with suboptimal eye-tracking and/or those in which the eye moved too tion. To ensure that stimuli remained at fixed locationsD on the retina, we discarded Sciences Reporting Summary appearance to allow the saccade to shift gaze normally. target of time the atHowever, off 2. turnedexperiment stabilizationwasin as stabilized retinally were location target possible the indicating boxes the and latterIntheneutral precededcue.and condition,wasby a fixationthemarker foveolaparafoveathe presentedthein targetorwasin experiments,either the instructed to look at the target as soon as it appeared. wereAs button.Observers ina pressing than the rather manualsaccade a making detectionby target the reportedbut observers 2),andexperiments detection(experiments 1 the in as target’s offset. the relativeto measured were times reaction experiments, all In ms. 100 only forandtarget andcue theless s,thethan both 2 were transiently presented for for visual fading to occur within the fovea. Stimuli were maintainedcontrast of visual stimulationon in theexperiments display2 and 3 did not allow enough time high durationand brief the stimuli,stabilized retinally prolongedto exposure observers were instructed not to press not to ( any 1 button. In experiment were instructed observers presentedwasneutral cue without followinga targetcatch In(19%).the trials, pointed cue in both directions (19%); and catch in which trials a directional or the which in trials neutral trials); all of targetlocation(15%and direction cue incongruentwith trials invalid trials); cue directional the of 76% and trials all presented: valid trials with congruent cue direction and target location (47% of two keys on a joypad as soon as the target was detected. Four types of trials were Fig. Fig. ata analysis. ata In all four experiments, observers were instructed to maintain their gaze at gaze maintaintheir to instructed were observers experiments,four all In ( 4 experiment In Discriminationexperiments Approximatelysamenumbersthe wereof trials discarded across subjectsin Detailed information about the experimental design can be found in the in experiment the In 3 ), but stimuli were not stabilized on the retina. They remained immobile at Performance was evaluated over trials with good retinal stabiliza Fig. Fig. Figs. 1 1 Figs. 4 Supplementary Figure 2 Figure Supplementary ), procedures were identical to those of experiment 3 < 200 ms and >2,000 ms in discrimination; less than and . In experiment 3 ( 3 experiment In . .

2 ). Supplementary Figure 1 Figure Supplementary Fig. Fig. 2 ), the target (5 arcmin × 5 arcmin) , the stimuli were the same the were stimuli the , Fig. Fig. 3 ), observers reported reported observers ), doi: 10.1038/nn.4622 shows that eye thatshows Fig. Fig. < 100 ms 100 1 ), the L ife - - - © 2017 Nature America, Inc., part of Springer Nature. All rights reserved. by Tukey by one-wayweremeansexaminedofby within-subjectstypes ANOVAs followed rank-sum tests and two-tailed Statistics. for each individual observer and summary statistics across observers. population the of majority the to generalizes N overreportedare statistics Summary ms). 700 or (400 targetand cue between delay the byfixation)nor, of2, (left/rightexperimentlocation target in the by affected neither were Results tests). rank-sum (Wilcoxon only independence ferences between valid and invalid trials using non-parametric tests that assumed center of the display. fixationsightofremainedthemarkerline targetto fromclose faratorthethe drift-only trials. Results also did not change when we selected trials in which the 3 not change when we eliminated these trials, as shown in analysis.themicrosaccadesincludedAgain, withwereinresults also trials did doi: by the data for two subjects, who were run extensively to collect large pools of = 5 observers, a sample size chosen to guarantee with In all reported experiments, all individual observers exhibited significant dif ( 4 experiment In 10.1038/nn.4622 posthoc Individual observers’ data were examined using two-tailed Wilcoxon tests. Comparisons between two conditions across observers Fig. Fig. 4 ), in which stimuli were not stabilized on the retina,thestimuli werestabilizednotonwhich in ), z -tests. Averages across observers in different trials 4 9 . All figures All . show average values Supplementary Figure P < 0.05 that the effect - 49. 48. 47. 46. request. reasonable correspondingauthoron the availablefrom is data analyze and collect to and C the corresponding author on reasonable request. D performed blind to the conditions of the experiments. were tested using two-tailed paired ode availability.ode ata availability. ata

Anderson, A.J. & Vingrys, A.J. Small samples: does size matter? cone foveal of variability Intersubject A. Roorda, & P. Tiruveedhula, K.Y., Li, N.M. Putnam, Crane, H.D. & Steele, C.M. Generation-V dual-Purkinje-image eyetracker. Vis. Sci. Vis. (2010). 6858–6867 length. eye to relation in density photoreceptor (2005). 632–639 24 , 527–537 (1985). 527–537 ,

42 , 1411–1413 (2001). 1411–1413 , t al. et The data sets generated and analyzed here are available from All the computer code used to implement the experiments implementthe to used computer code the All h lcs f xto ad h fva cn mosaic. cone foveal the and ﬁxation of locus The t -tests. Data collection and analysis were not net Ohhlo. i. Sci. Vis. Ophthalmol. Invest. NATURE NATURE NEUR Invest. Ophthalmol. OSCI Appl. Opt. . Vis. J. EN

51 C

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Supplementary Figure 1

Velocity of eye movements. Data represent averages across observers (n=5) for the cue-target intervals of Experiment 1 (parafovea; Fig. 1) and 2 (foveola; Fig. 2). In Experiment 2, stimuli were stabilized on the retina. (A) Average polar histograms of ocular drift velocity. (B) Mean instantaneous speed of ocular drift. Similar speed values were measured in the two experiments (p=0.63; two-tailed paired t-test). Error bars represent s.e.m. Time t=0 marks cue onset.

Nature Neuroscience: doi:10.1038/nn.4622

Supplementary Figure 2 Comparison between manual and oculomotor reaction times with stimuli in the parafovea and in the foveola. The two sets of data on the left (Manual) refer to the neutral trials of the detection experiments of Fig. 1 (parafovea; red) and Fig. 2 (foveola; blue). In these experiments, the observer reported the appearance of the target by pressing a button. For comparison, data points on the right (Saccade) show oculomotor reaction times in the neutral trials of similar experiments, but in which the target was reported by performing a saccade toward its location rather than by pressing a button. Reaction times are measured relative to target’s offset. Error bars are s.e.m. (n=4).

Nature Neuroscience: doi:10.1038/nn.4622

Supplementary Figure 3

Fine attentional control during normal retinal image motion (drift-only trials). Means ± s.e.m. for two individual subjects who were run extensively in Experiment 4 to collect sufficient numbers of trials without microsaccades (percentages of trials with microsaccades: 34%). Both subjects continued to exhibit significant differences between valid and invalid trials in both sensitivity (p<0.05, two-tailed z-test) and reaction times (p<0.05, ranksum test).

Nature Neuroscience: doi:10.1038/nn.4622

Supplementary Figure 4

Gaze position. Average histograms of eye position in the cue-target intervals of the discrimination experiments: (A) Experiment 3 (Fig. 3); and (B) Experiment 4 (Fig. 4), identical to Experiment 3, but without retinal stabilization. Data represent averages across observers (n=5).

Nature Neuroscience: doi:10.1038/nn.4622