The effects of crowding on eye movement patterns in reading_

The effects of crowding on eye movement patterns in readingEmanuela Bricolo a ,b ,⁎,Carola Salvi a ,Marialuisa Martelli c ,d ,Lisa S.Arduino e ,f ,Roberta Daini a ,baPsychology Department,University of Milano-Bicocca,Milano,Italy bMilan Center for Neuroscience,Milan,Italy cPsychology Department,University of Rome “La Sapienza ”,Rome,Italy dIRCCS Fondazione Santa Lucia,Rome,Italy eDepartment of Human Sciences,University LUMSA,Rome,Italy fInstitute of Cognitive Sciences and Technologies,ISTC-CNR,Rome,Italya b s t r a c ta r t i c l e i n f o Article history:Received 17April 2014Received in revised form 7June 2015Accepted 8June 2015Available online 2July 2015Keywords:Crowding ReadingEye movements SpaceCrowding is a phenomenon that characterizes normal periphery limiting letter identi fication when other letters surround the signal.We investigated the nature of the reading limitation of crowding by analyzing eye-movement patterns.The stimuli consisted of two items varying across trials for letter spacing (spaced,unspaced and increased size),lexicality (words or pseudowords),number of letters (4,6,8),and reading modality (oral and silent).In Experiments 1and 2(oral and silent reading,respectively)the results show that an increase in letter spacing induced an increase in the number of fixations and in gaze duration,but a reduction in the first fixation duration.More importantly,increasing letter size (Experiment 3)produced the same first fixation duration advantage as empty spacing,indicating that,as predicted by crowding,only center-to-center letter distance,and not spacing per se,matters.Moreover,when the letter size was enlarged the number of fixations did not increase as much as in the previous experiments,suggesting that this measure depends on visual acuity rather than on crowding.Finally,gaze duration,a measure of word recognition,did not change with the letter size enlargement.No qualitative differences were found between oral and silent reading experiments (1and 2),indicating that the articulatory process did not in fluence the outcome.Finally,a facilitatory effect of lexicality was found in all conditions,indicating an interaction between perceptual and lexical processing.Overall,our results indicate that crowding in fluences normal word reading by means of an increase in first fixation duration,a measure of word encoding,which we interpret as a modulatory effect of attention on critical spacing.©2015Elsevier B.V.All rights reserved.1.IntroductionThe relationship between eye-movements and reading has been studied for a long time.At the beginning of the 20th Century,Huey calculated that,while reading a text,the eyes move across the page (sac-cadic eye movements)at a nearly constant rate and that fluent adult readers make about four fixations per second (Huey,1908).As a conse-quence,the reading rate was thought to be the product of the number of fixations and the number of letters that could be acquired in each fixation (Woodworth,1938).Subsequently,O'Regan (1980)suggested that the amplitude of saccades in reading should be expressed as a num-ber of characters rather than as degrees of visual angle,and Morrison and Rayner (1981)showed that the average saccade amplitude remains constant at 5–6characters with increasing character size.Recently,it has been shown that crowding,a decoding impairment limiting the number of letters that can be processed in parallel in a glimpse,predicts reading rate (Pelli,Tillman,Su,Berger,&Majaj,2007).Crowding is a well-studied operationally de fined psychophysical phe-nomenon,whereby a letter is hardly identi fied when surrounded by nearby letters.The aim of this study is to show the eye-movement marker of crowding in functional reading.1.1.CrowdingBeyond acuity,letter recognition is impaired by crowding (for a review see Pelli,Palomares,&Majaj,2004;Levi,2008;Whitney &Levi,2011).This phenomenon,first named by Stuart and Burian (1962),has been explained in terms of the failure of the feature integration process within a spatial window (e.g.Parkes,Lund,Angelucci,Solomon,&Morgan,2001;Pelli et al.,2004).This window has been variously termed recognition span,perceptual span,visual span or uncrowded window (Legge,Mans field &Chung,2001;O'Regan,1990;Pelli et al.,2007;Rayner,1986).Pelli et al.(2007)showed that the visual span (i.e.,the number of letters that can be processed in a glimpse)corresponds to the size of the uncrowded window,namely,the letters that escape crowding at a given retinal eccentricity.The crowding effect is in fact related to the critical spacing between letters that is needed to restoreActa Psychologica 160(2015)23–34⁎Corresponding author at:Dipartimento di Psicologia,Universitàdi Milano-Bicocca,Edi ficio U6,Piazza dell'Ateneo Nuovo 1,20126Milano,Italy.E-mail address:emanuela.bricolo@unimib.it (E.Bricolo)./10.1016/j.actpsy.2015.06.0030001-6918/©2015Elsevier B.V.All rightsreserved.Contents lists available at ScienceDirectActa Psychologicaj o u r n a l h o me p a g e :w w w.e l s e v i e r.c o m /l o c a t e /a c t p s yrecognition.This spacing is roughly equal to half of the target viewing eccentricity(Bouma,1970).Bouma's proportionality of critical spacing with eccentricity means that feature integration failure is present almost always in the periphery.In fact,for the identification of a foveal letter,the integrationfield extends only through a few minutes of arc, which is close to the acuity threshold(Latham&Whitaker,1996), while the amplitude of the integrationfield increases together with ec-centricity but independently from visual acuity.Critical spacing is not linked to letter size per se nor to empty spacing per se,but it is center-to-center letter distance which limits letter recog-nition in crowding(Arditi,Knoblauch,&Grunwald,1990;Pelli et al., 2004;Strasburger,Harvey,&Rentschler,1991).With this in mind,we examined whether the effect of interletter spacing on eye movements during reading could be attributed to crowding.Indeed,when reading a text,some letters fall in the fovea,but most letters are located in the periphery.Since critical spacing scales with ec-centricity,there will be a point beyond which it will not be possible to identify the letters.The size of the uncrowded window for reading shrinks as it moves away from the foveal region(Chung,Mansfield,&Legge, 1998;Legge,Ahn,Klitz,&Luebker,1997;Legge,Mansfield,&Chung, 2001;Legge et al.,2007;Pelli et al.,2007).In afixed gaze condition,a pro-portional increase in spacing starting fromfixation allows crowding to be avoided because the letters pushed further into the periphery have pro-portionally increasing spacing needs.On the other hand,this proportional increase in spacing starting fromfixation is not feasible in an ecological reading context in which the eyes move continuously.Because of this, up to now,crowding has been studied almost exclusively withfixed gaze.We aimed to study the direct effect of crowding on the efficiency of reading by measuring eye movements in conditions of free viewing.In this condition,one possibility for partially reducing crowding is constant spacing.Indeed,while reading,some of the words will be seen parafoveally and increasing spacing at a constant rate would slightly move the crowding impairment towards the letters more in the periphery.Accordingly,it could be predicted that,in functional reading,when the eyes are free to move,an increase in letter spacing or letter size may similarly improve eye movement guidance by reducing the number offixations or/and the fixation duration.Two studies suggested the involvement of crowding in the effect of spacing on eye movements measures.McDonald(2006) found that a reduction of letter spacing,keeping constant the spatial width of word stimuli,increasedfixation duration.Hautala,Hyona,and Aro(2011)compared two different spacings given by proportional font and monospaced font.They found that the former,where an increase in the number of letters did not widen the word's spatial extent,induced an increase infixation duration and gaze duration with respect to the latter. Although Hautala et al.(2011)attributed this effect to the number of let-ters,both studies suggested a role of crowding infixation duration.1.2.Visual span,perceptual span,and the lexicality status of the stimuliThe visuo-spatial distribution of characters is relevant for the calculation and the programming of sacades,and the manipulation of both interletter and interword spacing greatly influences reading and saccadic eye movements(e.g.,Paterson and Jordan,2010;Pollatsek& Rayner,1982).McConkie and Rayner(1975)elegantly demonstrated that the amount of information that is used by the observer to guide saccades while reading extends for up to10characters to the right of fixation.However,when random letters are used,the span size is considerably lower than McConkie and Rayner's(1975)estimate. O'Regan(1990)proposed a distinction between the perceptual span that is obtained with words and that might be influenced by the lexical knowledge of the stimuli,and the visual span that is obtained with random letters(see Rayner,1986but also Legge et al.,1997,2001; Chung et al.,1998;Legge et al.,2007;Legge&Bigelow,2011).This suggests an interaction between perceptual and lexical com-ponents,during eye-movement guidance in reading.Thefirst step in reading aloud consists of the mapping of visual features onto representations through the computation of a set of letters that are displayed in a horizontal spatial orientation(McClelland& Rumelhart,1981,Rumelhart&McClelland,1982).This computation is probably achieved in parallel and represents a major challenge for word recognition models that need to incorporate visual limitations, such as crowding(e.g.,Coltheart,Rastle,Perry,Langdon,&Ziegler, 2001;Plaut,McClelland,Seidenberg,&Patterson,1996).In accor-dance to the dual route model of word recognition(DRC)proposed by Coltheart et al.(2001),while pseudowords are read via a slow grapheme-to-phoneme conversion strategy(GPC route),words can be read with both the GPC route and a less slow direct lexical matching(lexical route).According to the DRC model,reading aloud would be achieved in parallel using the lexical route and seri-ally using the grapheme-to-phoneme conversion rule(but see Zorzi, Houghton,&Butterworth,1998).The lexicality advantage may thus suggest that during reading,acquisition letter processing is opti-mized through a reduction in the size of the integrationfields with a consequent increase in the uncrowded window size expressed by a reduction in number offixation.However,if the perceptual limita-tion set by crowding constitutes a rigid bottleneck one might expect the same number of letters to be uncrowded when words and pseudowords are presented(Levi,2008;Pelli&Tillman,2008).In this case subjects may use a guessing strategy for words (e.g.,Paap,Newsome,McDonald,&Schvaneveldt,1982),producing different decoding times.In this vein,differences may be found in the fixation duration for these types of stimuli when crowding is relieved by increasing the spacing or size of letters.In the present study,we conducted three experiments in order to analyze the effects of interletter spacing,lexicality and number of characters on eye movements during reading.We developed a new two items reading task that allowed the testing of the effects of center-to-center letter distance(either by manipulating the letter spac-ing within a word or the font size).As in functional reading,in this task the reading pattern of the second item(the only one analyzed)is influ-enced by a previous similar item and not by afixed starting point(as in a single item reading task).In thefirst experiment,we recorded eye movements in normal readers by manipulating spacing and stimulus length while observers read words and pseudowords aloud.Although investigation of the complexities of oral compared to silent reading is out of the scope of the present paper,in the second experiment,in order to exclude the interference of time consuming articulatory processes,which could have slowed visual scanning,we asked new participants to perform the same task reading silently.The third experiment used the same stimuli and procedures as Experiment2,but manipulated character size rather than spacing.We hypothesized that if the observed changes are due to crowding and not to the insertion of empty interletter spacing per se,then manipulating size or spacing should lead to similar results.In particular,it has been shown that increasing spacing induces morefixations,reducesfixation duration and does not influence gaze duration(e.g.,Slattery&Rayner,2013).We hypothesized that the number offixations depends mostly on the string spatial extension. Thus,we predicted obtaining similar results on this parameter by increasing the number of letters or the spaces between them.In con-trast,we conjectured that the decrease infixation duration may reflect encoding and may be due to a release from crowding.In this vein,we predicted the same reduction infixation duration when increasing letter size or letter spacing.On the other hand,if the increase in the number offixations and the decrease infixation duration are due to spacing per se,the manipulation of size should not induce the same effects as the introduction of empty spacing.2.Experiment1:oral readingThefirst experiment was designed to study the effect of interletter spacing on eye movements.We required participants to read aloud.24 E.Bricolo et al./Acta Psychologica160(2015)23–34This allowed us to control for accuracy.We measured the effect of lexicality by comparing words and pseudowords.To maintain the exploratory behavior as close to functional reading as possible,we presented two-word stimuli in a row and analyzed only the second stimulus (target word).Finally,to allow correct identi fication of the last fixation on the target word,we added a secondary task consisting in the identi fication of a letter presented at the right edge of the screen.Observers were instructed to perform the letter identi fication task as fast as possible after reading the stimuli.2.1.Methods2.1.1.ParticipantsSixteen students at the University of Milano-Bicocca participated in the experiment (6males and 10females,mean age 22.4±2.9years).All participants had normal or corrected to normal vision (with contact lenses only),were native speakers of Italian and were skilled readers.Visual acuity was evaluated using the Lea SYMBOLS®charts (Hyvärinen,Näsänen,&Laurinen,1980).2.1.2.ApparatusParticipants'eye movements were recorded using a monocular video-based eye tracking system (ASL MODEL 5000,Applied Science Laboratories Inc.).Horizontal and vertical coordinates of the eye line of gaze were recorded at a 60Hz sampling rate and stored on a separate PC for of fline analysis.Eye position was measured with a spatial resolu-tion of about 0.5deg.Saccades were de fined as movements of the eyes between fixations.Fixations were de fined as periods when the line of gaze remained within a 0.5deg circle for at least 48ms.Eye blinks were detected as any abrupt “loss ”of the eye position signal.The stimuli were presented on a 19-in.Samsung SyncMaster 1200nf monitor with a 1024×768pixel resolution.Participants sat with their head supported by a chin rest and a forehead rest that was 67cm from the screen.Stimulus presentations and response recordings were controlled using a PC running E-Prime (Psychology Software Tools,Inc.,version 1.2).2.1.3.Materials and designStimuli were drawn in white on a black background (see Fig.1).In each trial the stimuli consisted of two items (both words or both pseudowords)rendered in Courier font with each character having a fixed size of 21×21pixels (0.70×0.70deg).The two items were separated by a 1.71deg empty space and presented horizontally in the center of the screen so that one word was displayed on the right side and the other word was displayed on the left side of the screen(see Fig.1).The 432words were selected from the LEXVAR database (Barca,Burani,&Arduino,2002).Pseudowords were constructed from words and at least two letters were changed in random positions to preserve pronunciation and minimize word similarity.Pseudowords were matched with words in character spacing and number of letters.Words and pseudowords were composed of 4,6and 8letters with 144items for each length.The stimuli were presented in two condi-tions:unspaced (standard)spacing (0pixel between characters;21pixels i.e.0.70deg center-to-center distance)and spaced (21pixels between characters;42pixels,i.e.1.40deg center-to-center distance).Stimuli with the same lexicality,length and spacing were paired in the same trial.The word and pseudoword stimuli were presented in differ-ent blocks and the order of the two blocks was counterbalanced across subjects.Spacing and length conditions were randomized in the two lists.Forty practice trials (20for each lexicality condition)were included at the beginning of each list and these trials were not considered in the analyses.2.1.4.ProcedureParticipants were informed that they would have to read words or pseudoword stimuli aloud and perform an identi fication task (sec-ondary task)of a letter that appeared at the right border of the screen and was vertically aligned with the stimuli (see Fig.1).Prior to the beginning of the experiment,a 9-point calibration procedure was performed.Calibration was checked before each trial and was repeated if necessary to reduce possible eye position measurement errors due to subject repositioning movements.After a successful calibration,the trials were presented.Subjects were instructed to fixate on the middle-left point of the calibration screen that was colored in red.As soon as their gaze was on this point,the trial began with the appearance of the stimuli.When participants completed reading,they were required to identify a letter,either an M or an N that was positioned at the extreme right side of the screen,by pressing one of two buttons.No response time limit was given to the participants.The experiment took approximately 25min to perform.2.2.ResultsOur focus was on the saccades falling on the second word of each stimulus pair.First fixation durations and landing coordinates for all fixations on the second word were extracted using an ad-hoc program in MATLAB.All trials with a loss of signal or a blink (12.6%;mean 27.3;SD 14),with m –n identi fication errors (1.5%;mean 3.2;SD 2.4)or with re fixations on the first word (2.8%;mean 6.1;SD 3.4)were discarded.The distribution of such missing data was comparable across experimental conditions.Reading errors were very few (3%;mean 6.6;SD 3.8).Overall,93.3%(SD 2.97)of the errors were made while partici-pants were reading non-words.In this condition no signi ficant differ-ences were found for unspaced (45.7%;SD 1.85)and spaced (47.6%;SD 1.84)non-words.Likewise no signi ficant difference was found for spaced (3.8%;SD.59)and unspaced (2.9%;SD.41)words.Number of er-rors increased proportionally to the number of letters only in the non-word condition (respectively for the unspaced condition:3.8%;SD .58for 4letter words,13.3%;SD .81for 6letter words and 28.6%;SD 1.41for 8letter words;for the spaced condition:4.8%;SD .6for 4letter words,12.4%;SD 1.28for 6letter words and 30.5%;SD 1.63for 8letter words).None of the comparisons across spaced and unspaced number of errors turn out signi ficant.The number of fixations,the first fixation duration and gaze duration for the second word were used as dependent variables.We chose,as a measure of word encoding,the first fixation duration because it is comparable across different word lengths.2.2.1.Number of fixationsFor each subject,the number of fixations was computed and entered into a repeated measures ANOVA with spacing (unspaced andspaced),Fig.1.Example of the stimuli used in Experiments 1,2and 3:Small unspaced stimuli above,small spaced stimuli in the middle and larger stimuli and pseudowords below.25E.Bricolo et al./Acta Psychologica 160(2015)23–34lexicality (words and pseudowords)and item length (4,6and 8letters)as the main factors.The number of fixations is reported in Table 1and plotted in Fig.2.All the main effects were signi ficant.The main effect of spacing [F(1,15)=113.27,p b 0.001]showed a signi ficantly larger number of fixations for spaced (mean 2.61)compared to unspaced stimuli (mean 1.90).The main effect of lexicality [F(1,15)=174.34,p b 0.001]showed more fixations for pseudowords compared to words (mean 2.68and 1.83,respectively).The main effect of item length [F(2,30)=120.65,p b 0.001]showed an increase in the number of fixations as the number of letters increased (4letters:mean 1.54;6letters:mean 2.30;8letters:mean 2.93).All two-way interactions were also signi ficant.The interac-tion between spacing and lexicality [F(1,15)=40.78,p b 0.01]emerged because spacing caused a larger increase in fixations for pseudowords (unspaced:mean 2.19;spaced:mean 3.17)compared to words (1.61compared to 2.06,unspaced and spaced,respectively).The interaction between spacing and item length [F(2,30)=22.05,p b 0.001],accord-ing to Scheffépost-hoc comparisons,emerged because spacing caused a larger increase in fixations for 6(p b 0.001)and 8(p b 0.001)letter words compared to 4(p b 0.001)letter words (spaced 4,6,8items:1.74,2.75,3.35,respectively;unspaced 4,6,8items:1.35,1.85,2.50,respectively).The interaction between lexicality and item length [F(2,30)=65.90,p b 0.001]was also signi ficant and re flected the higher number of fixations as item length increased for pseudowords compared to words.Scheffépost-hoc comparisons indicated that the number of fixations was higher for pseudowords compared to words for each length (p b 0.005).No other interactions were signi ficant.2.2.2.First fixation durationsFor each subject,the average first fixation duration for each stimulus was entered into a repeated measures 2×2×3ANOVA with spacing (unspaced and spaced),lexicality (words and pseudowords)and item length (4,6and 8letters)as the main factors.The first fixation duration is reported in Table 2and plotted in Fig.3.A signi ficant main effect of spacing [F(1,15)=31.64,p b 0.001]was found re flecting the shorter fixations for the spaced stimuli (188ms)compared to the unspaced stimuli (220ms).A signi ficant main effect of lexicality [F(1,15)=50.53,p b 0.001]was also found,which showed longer fixations for pseudowords (217ms)than for words (192ms).No other factors or interactions reached signi ficance.2.2.3.Gaze durationFor each subject,gaze duration (the sum of the duration of all fixations on the target word before the eyes leave that word)was computed and entered into a repeated measures 2×2×3ANOVA with spacing (unspaced and spaced),lexicality (words and pseudowords)and item length (4,6and 8letters)as the main factors.The gaze duration is reported in Table 3and plotted in Fig.4.All the main effects were signi ficant.The main effect of spacing [F(1,15)=29.47,p b 0.001]showed a signi ficantly longer gaze durationfor spaced (mean 470.92ms)compared to unspaced stimuli (mean 411.1ms).The main effect of lexicality [F(1,15)=167.38,p b 0.001]showed longer gaze duration for pseudowords compared to words (mean 543ms and 339.01ms,respectively).The main effect of item length [F(2,30)=85.06,p b 0.001]showed an increase in the gaze du-ration as the number of letters increased (4letters:mean 305.34ms;6letters:mean 440.98ms;8letters:mean 576.71ms).All two-way interactions were also signi ficant.The interaction between spacing and lexicality [F(1,15)=31.48,p b 0.001],according to Scheffépost-hoc comparisons,emerged because spacing induced longer gaze duration for pseudowords (unspaced:mean 493.47ms;spaced:mean 592.53ms;p b 0.001),but not for words (328.72ms compared to 349.31ms,unspaced and spaced,respectively;p =0.27).The interac-tion between spacing and item length [F(2,30)=5.31,p b 0.005],according to Scheffépost-hoc comparisons,emerged because spacing caused a longer gaze duration for 6(p b 0.001)and 8(p b 0.005)but not 4(p =0.23)letter stimuli compared to unspaced stimuli (spaced 4,6,8items:321.61ms,484.94ms,606.21ms,respectively;unspaced 4,6,8items:289.01ms,397.02ms,547.21ms,respectively).The inter-action between lexicality and item length [F(2,30)=52.29,p b 0.001]was also signi ficant and re flected,according to Scheffépost-hocTable 1The table reports means ±SE for the number of fixations for all experimental conditions for all experiments.Pseudowords Words 468468Experiment 1:Spacing aloud Crowded 225.3±8.9229.6±10.0247.7±12.4196.6±9.0208.6±10.6213.7±10.0Uncrowded 194.4±9.2202.6±9.0202.4±10.5180.1±8.9175.6±7.6174.9±6.7Experiment 2:Spacing silent Crowded 222.5±7.9231.3±8.7212.1±9.4193.9±7.2193.0±6.8197.2±7.4Uncrowded 181.1±7.6169.2±5.9167.2±5.5176.9±6.3170.7±4.7165.5±6.0Experiment 3:Size silent Crowded 220.7±13.2238.5±13.8225.3±11.3179.3±7.0188.89±7.0195.0±9.5Uncrowded197.4±11.1180.2±9.1171.7±8.9173.4±8.3169.1±6.6157.2±7.4Fig.2.Experiment 1:The number of fixations (±1SE)as a function of item length for the reading aloud of words (black squares)and pseudowords (red circles).Results for the standard spacing condition are shown as open symbols;results for the spaced condition are shown as filled symbols.26 E.Bricolo et al./Acta Psychologica 160(2015)23–34comparisons,that the increase in gaze duration as item length increased was higher for pseudowords compared to words for each length (p b0.001).No other interactions were significant.3.DiscussionThe results show that increasing spacing affected each one of the variables considered in the study:the number offixations and the gaze duration increased,while thefirstfixation duration decreased.The number offixations increased as a function of stimulus length both in terms of the number of letters and spacing.The gaze duration followed the number offixations.Thefirstfixation duration decreased with the increase in spacing,to a value of around20–25%less than the usualfixation duration obtained in most eye movement studies.This latterfinding,other than being consistent with recentfindings on the effect of spacing on reading(Bai,Yan,Liversedge,Zang,&Rayner, 2008,Kohsom&Gobet,1997;Paterson&Jordan,2010;Sainio,Hyönä, Bingushi,&Bertram,2007),could be explained by the fact that spacing induces a release in crowding,which is responsible for a reduction in the decoding time.An alternative explanation for the decrease infirstfixation duration in the spaced condition could be that this variable is not independent from the number of saccades.If this was the case,we would have observed complementary effects on the two measures in all conditions and no gaze duration increase.However,the two measures behaved differently from each other in different conditions:the number of fixations was sensitive to the item length whilefirstfixation duration was not.Both measures were sensitive to lexicality in the same direc-tion(both increasing for pseudowords),while they are affected by spacing in opposite directions.Our results are in agreement with the idea that an increase infixa-tion time may,at least in part,be due to greater task difficulty,which is reflected in the oculomotor programming of saccades(Kowler& Anton,1987).The longerfirstfixation duration for unspaced stimuli is consistent with the idea that in this case encoding is limited by crowding.Finally,the increase in the number offixations,as in gaze duration, with the increase in item length was higher for pseudowords than for words.The present results may represent the outcome of two different types of processing,similar to the dual route model proposed by Coltheart et al.(2001).In this case,the engagement of the nonlexical route,which is considered to be serial,would activate a different oculo-motor behavior to the parallel analysis that is involved in the use of the lexical route(see also Paap et al.,1982).The absence of an interaction between lexicality and spacing infirst fixation duration suggests that the mechanisms underlying the two effects are independent.Words may be encoded faster because fewer features are needed to identify the letters in words;firstfixation dura-tion may be shorter for spaced compared to unspaced letters because the features are relieved from crowding.The lack of interaction may imply that crowding imposes a hard limit on the visual content that is available for higher level processing,irrespective of stimulus type.4.Experiment2:silent readingIn Experiment1,subjects read the stimuli aloud and the results show that they were quite accurate.Nevertheless,it is possible that this modality lowered reading speed and altered the eye movement pattern.To exclude the articulatory component and make the task more similar to everyday reading,we replicated the conditions but asked the subjects to read silently.Previous research has found that reading silently and reading aloud differ quantitatively but not qualita-tively in terms of parafoveal information facilitatory effects(Ashby, Yang,Evans,&Rayner,2012).Accordingly,we expected quantitative, but no qualitative effects,on relevant variables such as lexicality and spacing.4.1.Methods4.1.1.ParticipantsSixteen students at the University of Milano-Bicocca participated in the present experiment(2males and14females,mean ageTable2The table reports mean±SEfirstfixation duration for all conditions for all experiments.Pseudowords Words468468Experiment1:Spacing aloudCrowded225.3±8.8229.6±10.0247.6±12.4196.6±9.0208.6±10.7213.7±10.0 Uncrowded194.4±9.2202.6±9.0202.4±10.5180.1±8.9175.5±7.6174.9±6.7Experiment2:Spacing silentCrowded222.5±7.9231.2±8.7212.1±9.4193.9±7.2193.0±6.7197.2±7.4 Uncrowded181.1±7.6169.1±5.9167.2±5.5176.9±6.3170.7±4.7165.5±6.0Experiment3:Size silentCrowded220.7±13.2238.5±13.8225.3±11.3179.3±7.0188.9±7.0195.0±9.5Uncrowded197.4±11.1180.2±9.0171.7±8.9173.4±8.3169.1±6.6157.2±7.4Fig.3.Experiment1:The meanfirstfixation duration(±1SE)as a function of item length for the reading aloud of words(black squares)and pseudowords(red circles).Results for the standard spacing condition are shown as open symbols;results for the spaced condi-tion are shown asfilled symbols.27E.Bricolo et al./Acta Psychologica160(2015)23–34。