Inhibition of return and attentional facilitation: Numbers can be counted in, letters tell a different story

Acta Psychologica 163 (2016) 74–80

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Inhibition of return and attentional facilitation: Numbers can be counted in, letters tell a different story Danielle Hoffmann a,⁎, Valérie Goffaux b, Anne-Marie Schuller c, Christine Schiltz c a b c

Research and Transfer Centre LUCET, FLSHASE, University of Luxembourg, Luxembourg Research Institute IPSY, Université Catholique de Louvain, Belgium Research Unit ECCS, FLSHASE, University of Luxembourg, Luxembourg

a r t i c l e

i n f o

Article history: Received 9 December 2014 Received in revised form 21 September 2015 Accepted 17 November 2015 Available online xxxx Keywords: Attention Inhibition of return Numbers Automaticity

a b s t r a c t Prior research has provided strong evidence for spatial–numerical associations. Single digits can for instance act as attentional cues, orienting visuo-spatial attention to the left or right hemifield depending on the digit's magnitude, thus facilitating target detection in the cued hemifield (left/right hemifield after small/large digits, respectively). Studies using other types of behaviourally or biologically relevant central cues known to elicit automated symbolic attention orienting effects such as arrows or gaze have shown that the initial facilitation of cued target detection can turn into inhibition at longer stimulus onset asynchronies (SOAs). However, no studies so far investigated whether inhibition of return (IOR) is also observed using digits as uninformative central cues. To address this issue we designed an attentional cueing paradigm using SOAs ranging from 500 ms to 1650 ms. As expected, the results showed a facilitation effect at the relatively short 650 ms SOA, replicating previous findings. At the long 1650 ms SOA, however, participants were faster to detect targets in the uncued hemifield compared to the cued hemifield, showing an IOR effect. A control experiment with letters showed no such congruency effects at any SOA. These findings provide the first evidence that digits not only produce facilitation effects at shorter intervals, but also induce inhibitory effects at longer intervals, confirming that Arabic digits engage automated symbolic orienting of attention. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Numbers are omnipresent in our daily lives. We use them for instance to express the value of a given item, to indicate time, dates and locations, to evaluate distances, quantities and order. Behavioural studies have shown a strong link between number and space representations (for a review, see de Hevia, Vallar, & Girelli, 2008; Fias & Fischer, 2005; Hubbard, Piazza, Pinel, & Dehaene, 2005). A popular hypothesis states that the representation of numerical magnitude is mapped onto a spatial mental number line (Dehaene, 1992; Moyer & Landauer, 1967; Restle, 1970) oriented from left to right — at least in western cultures (Dehaene, Bossini, & Giraux, 1993). Whereas most people are unaware of this association of numerical and spatial representations, approximately 12% of individuals (Tang, Ward, & Butterworth, 2008) experience this number–space link consciously: number–form synaesthetes (Galton, 1880; Hubbard, Ranzini, Piazza, & Dehaene,

⁎ Corresponding author at: Research and Transfer Centre LUCET, FLSHASE, University of Luxembourg, Maison des Sciences Humaines, 11, Porte des Sciences, L-4366 Esch-surAlzette, Luxembourg. E-mail address: [email protected] (D. Hoffmann).

http://dx.doi.org/10.1016/j.actpsy.2015.11.007 0001-6918/© 2015 Elsevier B.V. All rights reserved.

2009; Jarick, Dixon, Maxwell, Nicholls, & Smilek, 2009; see Price & Mattingley, 2013 for a review). The best-documented demonstration of the association of numbers and space is the so-called SNARC effect (Spatial–Numerical Association of Response Codes), first described by Dehaene et al. in 1993 (for a review see Fias & Fischer, 2005). The SNARC effect refers to the observation that in a magnitude irrelevant binary classification task on centrally presented digits, participants are typically faster to respond to a small number with the hand in their left side of space, and to a large number with the hand in the right side of space. These findings were interpreted as reflecting the specific orientation characteristics of the mental number line representation stored in long-term memory (for a meta-analysis see Wood & Fischer, 2008). Alternatively, the effect has been proposed to reflect the direction of serial order processing in working memory (van Dijck & Fias, 2011; van Dijck, Abrahamse, Acar, Ketels, & Fias, 2014; van Dijck, Abrahamse, Majerus, & Fias, 2013). The association between numbers and space has been confirmed by behavioural evidence that numbers can shift visuo-spatial attention when they are presented as uninformative cues in the context of a target detection task (Fischer, Castel, Dodd, & Pratt, 2003). Fischer and colleagues reported that participants were faster to detect a left-sided target when it was preceded by a small digit, whereas

D. Hoffmann et al. / Acta Psychologica 163 (2016) 74–80

right-sided targets were detected faster when preceded by a large digit; even though the digit was presented centrally and was completely irrelevant to the successful completion of the target detection task. These findings are referred to as “attentional SNARC effect” (e.g. Dodd, van der Stigchel, Adil Leghari, Fung, & Kingstone, 2008; van Dijck et al., 2014). More recently, neuroscientific studies have extended the attentional SNARC effect to modulations of neural activity using functional magnetic resonance imaging (fMRI) (Goffaux, Martin, Dormal, Goebel, & Schiltz, 2012) and eventrelated potential (ERP) techniques (Ranzini, Dehaene, Piazza, & Hubbard, 2009; Salillas, El Yagoubi, & Semenza, 2008; Schuller, Hoffmann, Goffaux, & Schiltz, 2014). Since in the original paradigm, digit cues were task-irrelevant and non-predictive of target location it has been suggested that visuo-spatial attention shifts induced by numbers are obligatory. However several more recent reports (Galfano, Rusconi, & Umilta, 2006; Ristic, Wright, & Kingstone, 2006) indicate that the observed visuo-spatial attention shifts induced by numbers are influenced by the participant's mental set, and thus question the automaticity of attentional shifts elicited by digits. As a matter of fact, it was reported that number-induced attentional shifts can be abolished by simply adding vertical target locations. The attention effect is even reversed when asking participants to imagine a mental number line running from right to left or a clock face (Ristic et al., 2006) or when instructing participants to orient their attention to the left after large numbers and to the right after small numbers (Galfano et al., 2006; for a detailed discussion about the issue of automaticity of visuo-spatial cueing by numerals see Galfano et al., 2006 and Ristic et al., 2006). Contrary to the above-mentioned hypothesis of obligatory attentional shifts, these findings suggest that activation of the mental number line is influenced by top-down control (see also Zanolie & Pecher, 2014 for a failure to replicate the original study and the related comment by Fischer & Knops, 2014). Classically the visuo-spatial attention field distinguished “exogenous” attentional processes, following salient peripheral cues controlled exclusively by the external events themselves, from “endogenous” ones, induced by internal expectations following central and predictive cues (James, 1890; Jonides, 1981; Posner, 1980; Posner & Cohen, 1984; Yantis & Jonides, 1984). Exogenous cues typically induce a facilitation effect (i.e. shorter RTs for cued targets than uncued targets) followed by inhibition of return (IOR) (Posner & Cohen, 1984; Posner, Rafal, Choate, & Vaughan, 1985) at longer cue-target intervals at the cued location. IOR refers to the fact that cued targets are processed slower than uncued targets at long cue-target intervals since after the initial attentional shift, attention is subsequently disengaged from that location in order to facilitate visual search (see Klein, 2000 for a review). With endogenous (predictive) cues, initial facilitation is in comparison slow to emerge and long lasting — typically without being followed by an IOR effect (Taylor & Klein, 2000; but see Lupiáñez, Martín-Arévalo, & Chica, 2013 for a report of IOR using an endogenous cueing paradigm). IOR is thought to arise because people tend not to revisit recently attended locations (Posner et al., 1985; Posner & Cohen, 1984 in Mathôt & Theeuwes, 2010). It was also proposed that IOR might be related to oculo-motor response preparation (e.g. Rafal, Calabresi, Brennan, & Sciolto, 1989; but see also Chica, Klein, Rafal, & Hopfinger, 2010) and sensory adaptation processes (e.g. Berlucchi, 2006; Posner & Cohen, 1984). In the last decade, this overly simple sub-categorisation into endogenous vs. exogenous attention effects has been revisited (Chica & Lupiáñez, 2009; Chica, Lupiáñez, & Bartolomeo, 2006; Hommel, Pratt, Colzato, & Godijn, 2001; Lupiáñez et al., 2004; Pratt & Hommel, 2003; Ristic & Kingstone, 2006, 2009, 2012; Ristic, Landry, & Kingstone, 2012; Ristic, Wright, & Kingstone, 2007; see also Gibson & Kingstone, 2006). A more descriptive and balanced classification of attentional cues has been elaborated by focusing (a) on the informational content of the cue (predictive vs. non-predictive) and (b) on its spatial position

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with respect to visual fixation (central vs. peripheral). Amongst others, the traditional focus on central predictive cues was balanced by using also central non-predictive cues that convey spatial information.1 Accordingly Ristic and Kingstone (2012) recently extended the prevailing framework by suggesting a third form of attentional orienting processes to account for attentional effects induced by central uninformative but behaviourally relevant cues. In their study, the authors demonstrate that overlearned behaviourally relevant stimuli engage attentional orienting processes that operate independently of, and in parallel with, endogenous and exogenous spatial attention. Ristic and Kingstone refer to these processes as automated symbolic orienting as they reflect an “involuntary attentional response that has become automated as a function of repeated exposure to environmental contingencies”, with the term “automated” reflecting the learning aspect of this automatic effect. Consequently, the automaticity of the effect may vary as a function of central cue (Ristic & Kingstone, 2012). The attentional response is described as being involuntary or unintentional as opposed to endogenous orienting, which is based on intentional resource allocation and exogenous orienting which occurs without intention but as a function of simple sensory stimulation. Automated symbolic orienting arises without intention but as a function of the overlearning of the cue's contingency over time (Dodd & Wilson, 2009). In the cue category eliciting automated symbolic orienting, Ristic and Kingstone distinguish between social biologically relevant cues such as gaze (Driver et al., 1999; Langton & Bruce, 1999) and finger pointing (Langton & Bruce, 2000) and nonsocial behaviourally relevant cues such as arrows (Hommel et al., 2001; Ristic, Friesen, & Kingstone, 2002; Tipples, 2002). Pertinent to the present study, former research has indicated that the facilitation effects produced by this type of cues can be followed by IOR. With gaze cues IOR has been observed when using particularly long stimulus onset asynchronies (SOAs) (Frischen & Tipper, 2004; Frischen, Bayliss, & Tipper, 2007; Frischen, Smilek, & Tipper, 2007; Jingling, Lin, Tsai, & Lin, 2015; Marotta et al., 2013), whereas central arrows have been shown to lead to IOR in the context of saccade preparations (Rafal et al., 1989, but see Chica et al., 2010) or for specific response modalities (manual versus saccadic, see Taylor & Klein, 2000). As mentioned above, several studies have also shown that digits orient visuo-spatial attention when they are presented as central nonpredictive cues in lateral target detection paradigms (Fischer et al., 2003; Galfano et al., 2006; Ristic et al., 2006). However, so far none of these studies investigated potential IOR effects expected at longer SOAs for this nonsocial behaviourally relevant type of central nonpredictive cue as has been done with social biologically relevant cues (see Frischen & Tipper, 2004; Frischen, Bayliss, et al., 2007; Frischen, Smilek, et al., 2007; Jingling et al., 2015; Marotta et al., 2013). The current study fills this gap by investigating attentional SNARC effects at short and long SOAs, thus exploring the time course of attentional orienting effects induced by central non-informative digits. Since IOR has been observed with social biologically relevant eye-gaze cues and nonsocial behaviourally relevant arrow cues, we might also expect IOR after non-predictive centrally presented digit cues when using appropriately long SOAs. The present design thus provides important information on the automated nature of attention shifts associated with digits, originating from the category of non-social behaviourally relevant cues. Our findings will critically help define this central nonpredictive cue type that has been reported to elicit less automatic effects than for instance gaze cues (Galfano et al., 2006). Our control condition consisted of the same paradigm using letters of the alphabet as central non-predictive cues. It has been shown that other ordered series such as letters are associated to space (Gevers,

1 In addition to the classically used uninformative peripheral cues, Lupiañez and colleagues also introduced informative peripheral cues and found facilitation followed by IOR for predictive as well as non-predictive peripheral cues. This finding indicates that expectations based on cue predictiveness do not influence involuntary attention shifts induced by peripheral cues (Chica & Lupiáñez, 2009; Lupiáñez et al., 2004, 2013).

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Reynvoet, & Fias, 2003; see also van Dijck et al., 2014) but do not orient attention when passively viewed (Dodd et al., 2008). Therefore we expected that the behaviourally encountered association of this ordered series to space would be less strong than the associations between numbers and space and hence the attentional symbolic orienting, which they entail, should be less automated. We therefore specifically and exclusively expected attentional facilitation effects followed by IOR for the digit cues. The confirmation of our hypothesis would provide evidence for an unintentional nature of visuo-spatial orienting associated with digit cues and would further corroborate the assumption that digits belong to the same family of stimuli inducing automated symbolic orienting as other central symbolic cues such as arrows or gaze (even though probably at another end of the same spectrum, as proposed by Ristic et al., 2006). The association of another ordered series (letters) to space on the other hand might prove to be less strong and thus unable to induce automated symbolic orienting. 2. Methods 2.1. Participants Fifty-one volunteers (mean age: 21.7 years, 13 males, 4 left-handers) were paid to participate in the study. They all reported to have normal or corrected-to-normal vision, and were naïve as to the purpose of the study. Twenty-six subjects participated in the digit experiment and the remaining twenty-five enrolled in the letter experiment. 2.2. Procedure Participants were seated at a distance of approximately 57 cm from a 19-in. colour monitor (800 × 600 pixels) in a quiet, darkened room. The task was programmed in E-prime (Schneider, Eschmann, & Zuccolotto, 2002). Fig. 1 illustrates the stimuli and the task events. Each trial began with the display of a dark blue central cross (presented in 28-point Arial bold font) on a light gray screen, with two lateral black boxes (6.3 × 3.9 cm) aligned with the horizontal meridian.

Fig. 1. Illustration of the experimental sequence. At the beginning of each trial a central fixation cross was displayed for 500 ms then a digit/letter cue appeared for 400 ms in the digit/letter condition, respectively. The digit/letter cue was replaced by another central fixation cross, displayed for a variable ISI (100, 250, 500, 750, 1000 or 1250 ms), resulting in SOAs of 500, 650, 900, 1150, 1400 or 1650 ms respectively, until the target (red or green asterisk) appeared briefly (100 ms) in the left or right lateral box. Finally the initial screen with the central cross reappeared and lasted for a variable ITI (1200, 1500 or 1800 ms). Note: Stimuli are not drawn to scale. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Their outer edges were located approx. 2.2 cm (i.e. 2.2°) to the left and right from the centre of the screen. After 500 ms, the fixation cross was replaced with one of four possible cues presented in 28-point Arial bold font in black colour. In the digit condition numbers 1, 2, 8 or 9 were presented, whereas A, B, Y and Z were used in the letter condition (based on Dodd et al., 2008). The cue was displayed for 400 ms and then replaced by a black central cross (identical to the initial one, except for its colour). After a random inter-stimulus interval (ISI) (100, 250, 500, 750, 1000 or 1250 ms) on 89.9% of the trials, a target (red or green asterisk) appeared briefly (100 ms) in the centre of either the left or the right lateral box. The remaining 11.1% of the trials were catch trials, in which no target appeared, and no response was required. Participants were instructed to fixate the centre of the screen throughout each trial, and to press the response key as fast as possible once the target had appeared. Participants were told that the digit/letter cue was completely irrelevant to the task, and that the side on which the target appeared was random. Responses were given by pressing the “B” key of a standard “QWERTZ” keyboard, connected to a Dell Optiplex GX620 computer, recording responses and RTs. Each block began with 10 practice trials; the experiment itself consisted of 2 blocks of 267 trials each, administered in two different experimental sessions on two different days. After each series of 24 trials, a feedback screen informed participants on the percentage of correct responses. This screen stayed on for 8000 ms, allowing participants to take a short break. 2.3. Statistical analyses Prior to data analyses, catch trials (n = 54) and misses (digit condition: 0.95%; letter condition: 1.63%) were removed from the recorded reaction times (RT). All RTs longer or shorter than 2.5 standard deviations from the individual mean were considered outliers (digit condition: 2.15%; letter condition: 2.36%) and removed. In the digit condition, the data of one outlier participant were excluded from the analyses as his RTs differed significantly (N2.5 standard deviations) from the other participants. The trimmed data of the remaining 50 participants were submitted to the statistical analyses. To investigate how SOA influenced attentional modulation, we used linear regression analysis methods for repeated measures data recommended by Lorch and Myers (1990). This approach was suggested by Fias and colleagues (Fias, Brysbaert, Geypens, & d'Ydewalle, 1996; see also van Galen & Reitsma, 2008), as digit magnitude is a continuous variable, and the (attentional) SNARC effect is thought to reflect the link between digit magnitude and a spatial code. It provides an individual score, and allows thus to better appreciate the presence or absence of an attentional SNARC effect in each participant. In each individual subject, we calculated mean RTs for each digit/letter, target side and SOA separately. We then computed individual RT difference scores (dRT) by subtracting for each digit/letter the mean RT of right-sided target detection from the mean RT of left-sided target detection. The obtained dRT scores were submitted to a regression analysis, using digit magnitude/letter position in the alphabet as predictor variable. This procedure provides individual regression weights of each participant, reflecting the strength of their attentional SNARC for digits and letters. First, we investigated how the attentional SNARC effects were modulated by SOA in the two different cueing conditions (digits vs. letters). A 2 × 6 repeated measures analysis of variance (ANOVA) was performed on individual regression weights with SOA (500 ms, 650 ms, 900 ms, 1150 ms, 1400 ms or 1650 ms) as within subject factor and cueing condition (digits, letters) as between subjects factor. An interaction between cueing condition and SOA would reveal differential attentional SNARC effects due to digits as compared to letters (in line with our hypothesis), whereas an absence of this interaction would rather point to identical attentional effects. To further investigate the expected significant interaction between cueing condition and SOA, separate repeated-measures ANOVAs were computed for each cueing condition (i.e. digits and letters). Within

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cueing conditions, a main effect of SOA indicates a modulation of slope values as a function of SOA. Second, linear within-subjects contrasts of SOA on slope values were considered. These latter contrasts optimally illustrate the gradual linear change in slope values over time (SOA) and consequently reveal best how attention orienting progressively and linearly changes from initial facilitation to later IOR. Finally, significant main effects of SOA (expected with digit cues) where further characterized using planned comparisons to determine whether the regression weights differed significantly from zero. We expected to find significant negative slopes revealing facilitation at short SOAs (i.e. SOA 650 ms) in line with previous studies (e.g. Fischer et al., 2003; Ristic et al., 2006) whereas the slopes for longer SOAs (i.e. SOA 1650 ms) should be significantly positive, reflecting longer RTs to detect a left/right sided target after small/large digits due to IOR. 3. Results and discussion Consistent with our expectations, we found a significant interaction between cueing condition (digit vs. letter) and SOA, F(5240) = 2.32, p = 0.04, η2 = 0.05. Performing a repeated-measures ANOVA on regression weights separately for each cueing condition revealed a significant main effect of SOA when digits were used as cues, F(5120) = 2.5, p = 0.03, η2 = .094. Specifically with digit cues, slope values turned from negative values at short SOAs (reflecting attentional facilitation) to positive values at long SOAs (reflecting IOR)2 (see Fig. 2). Hence, the standard attentional SNARC effect observed at short SOAs (i.e. faster left/ right target detection advantage after small/large digits respectively) was reversed at long SOAs (i.e. faster right/left target detection after small/large digits respectively). No such effect was observed using letter cues, F(5120) = 0.15, p = 0.98, η2 = 0.006. The change in strength and direction (facilitation vs. IOR) of the attentional SNARC effect as a function of SOA duration, is reflected by a linear within-subjects contrast. When digits were used as central cues, slope values progressively and linearly evolved from negative to positive values with increasing SOAs, F(1, 24) = 5.58; p = 0.027, η2 = 0.19, indicating that the attentional effect gradually changed from facilitation to IOR (see Fig. 2). As expected, planned comparisons confirmed that the negative slope value differed significantly from zero at SOA 650 ms, t(24) = 1.7; p = 0.05 (one-tailed), indicating early attentional facilitation. And critically, the significantly positive slope at SOA 1650 ms, t(24) = 2.7; p b .01 (one-tailed), confirmed that facilitation was followed by IOR at long cue-target intervals. For letters in contrast, slope values did not change over the different SOAs, F(1, 24) = 0.24; p = 0.63, η2 = 0.01. In summary, when using Arabic digits as spatially uninformative attentional cues we observed that facilitation of congruent target detections at short SOAs was followed by IOR at longer SOAs. To the best of our knowledge, these findings provide the first evidence that digits not only produce facilitation effects at short cue-target intervals, but also induce inhibitory effects at longer intervals, similar as has been observed with arrows (Rafal et al., 1989) or gaze (Frischen & Tipper, 2004; Frischen, Bayliss, et al., 2007; Frischen, Smilek, et al., 2007; Jingling et al., 2015; Marotta et al., 2013), when used as central uninformative attentional cues. Facilitation and IOR were specific to numerical magnitude, as the effects failed to generalize to other ordered series as letters of 2 These results were confirmed by the two-way repeated-measures ANOVA on RTs testing for congruency [congruent (=left/right target after small/large digit) vs incongruent (=left/right target after large/small digit) condition] and SOA for digits. This analysis yielded a significant main effect of SOA since RTs were shorter at longer SOAs, F(5120) = 56.32, p b 0.001, η2 = 0.7, most likely indicating a foreperiod effect (Mowrer, 1940, in Ristic et al., 2006). There was no main effect of congruency, F(1,24) = 0.24, p = 0.63, η2 = 0.01. But critically, the interaction between congruency and SOA was significant, F(5120) = 2.3, p = 0.049, η2 = 0.09. In other words, SOA selectively modulated the number–space congruency effects, such that congruent targets were detected faster at short SOAs, whereas longer SOAs led to increased RTs for congruent targets.

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the alphabet, indicating a special role of numerical magnitude in the context of target detection tasks using uninformative central symbolic cues. 4. General discussion In the present study we manipulated the temporal interval separating number and letter cues from lateral targets (SOA 500–1650 ms) in a detection task in order to cover both the emergence of early facilitation and potential late IOR effects in spatial orienting. Using digits as cues, we found a facilitation effect of target detection at short SOAs (650 ms) of the same order as previous studies when cue magnitude and target side were congruent (Fischer et al., 2003; Galfano et al., 2006; Ristic et al., 2006). Left targets were detected faster after small digits, whereas large digits speeded up detection of right targets. In addition and for the first time, we also observed that facilitation turned into IOR with increasing SOA durations. This evolution from facilitation to IOR was best captured by the statistically significant regression analysis plotting slope coefficients as a function of SOAs. Investigations concerning the time-course and automaticity of attentional effects induced by nonsocial, behaviourally relevant central uninformative cues (here digits and letters) are of crucial importance to better understand the orienting nature of this type of cues. The observation that central, spatially non-informative digits elicit visuo-spatial attention shifts in participants initially led Fischer and colleagues to the conclusion that these shifts might be obligatory (Fischer et al., 2003). Later studies then found that these shifts can be easily overruled by the participants (e.g. the task setting or their mental set) and made it evident that left-ward shifts after small digits and rightward shifts after large digits are not immune to top down control (Galfano et al., 2006; Ristic et al., 2006). However, such high influence of voluntary control is not limited to attentional orienting associated with digit cues, but compatible with other reports that highlight the impact of voluntary control on unintentional attention orienting. Studies investigating the automaticity of attentional capture by uninformative peripheral cues suggest that attentional capture can be considered as being automatic “by default”, i.e. in the absence of a specific mental set (see Ruz & Lupiáñez, 2002 for a review). However, specific task- or mental sets allow overcoming this unintentional orienting in a topdown manner (e.g. Folk, Remington, & Johnston, 1992; Pratt & Hommel, 2003; Warner, Juola, & Koshino, 1990). Similarly, the visuospatial attention orienting we observed with passively viewed uninformative digits might reveal the default number–space association that participants have, at least in western countries. The finding that digit (but not letter) cues induced facilitation and IOR clearly a) assimilates the former to the category of central nonpredictive stimuli that produce automated symbolic orienting effects of attention (Ristic & Kingstone, 2012) such as arrows and eye gaze (Frischen & Tipper, 2004; Frischen, Bayliss, et al., 2007; Frischen, Smilek, et al., 2007; Jingling et al., 2015; Marotta et al., 2013; Rafal et al., 1989) and b) indicates that digit series are more intrinsically linked to space than other ordered series such as letters. Consequently only passively viewed digits but not letters produce automated symbolic orienting effects. Since the level of automaticity varies as a function of behavioural contingencies, our findings indicate that the link between space and digits is more frequently encountered than the link between space and other ordered series, such as letters. Ristic et al. (2006) propose that there is a range of stimuli that can produce “reflexive” shifts of attention, with abrupt peripheral onsets at one end of the spectrum, and numbers at the other end (Ristic et al., 2006). According to the level of their biological relevance and the rigidity of their left–right polarity, the former tend to be obligatory and rapid, whilst the latter are much slower and can more easily be overridden by voluntary control (for a similar account see also Galfano et al., 2006). Recently Ristic and Kingstone (2012) further extended the classical theoretical framework of attentional orienting (exogenous

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Fig. 2. Evolution of regression weights from negative to positive as a function of SOA with digit, but not letter cues.

vs. endogenous) by describing a third process, namely automated symbolic orienting, induced by central non-predictive cues. Whereas it is known that cues such as briefly flashed peripheral stimuli (Posner & Cohen, 1984) as well as gaze (Frischen & Tipper, 2004; Frischen, Bayliss, et al., 2007; Frischen, Smilek, et al., 2007; Jingling et al., 2015; Marotta et al., 2013) are able to induce IOR effects (for a review see Klein, 2000), we provide the first evidence that numbers can also induce IOR at longer SOAs. This finding implies that whenever a digit-induced shift of visuo-spatial attention occurs, it is quite long-lasting (up to 1650 ms in the present study) and follows the pattern described with unintentional visuo-spatial attention cues. The present data consequently provide important insights into the nature of central uninformative digits as nonsocial behaviourally relevant visuo-spatial attention cues inducing automated symbolic orienting effects and thus strengthen their classification within the above-mentioned taxonomy. One striking difference that can be observed between IOR in the two unintentional orienting processes (i.e. exogenous orienting and automated symbolic orienting) is the time-course. Whereas facilitation occurs very rapidly in exogenous cueing (at around 100 ms) and is followed by IOR at around 300 ms, the time-course in automated symbolic orienting is much slower. Facilitation starts occurring between 100 and 200 ms for gaze cues and arrows (Friesen & Kingstone, 1998; Ristic et al., 2002) and around 600 to 700 ms for digits (Fischer et al., 2003; Ristic et al., 2006). IOR with central cues has been reported at various SOAs: at 1000 ms for arrow cues (e.g. Taylor & Klein, 2000) and 2400 ms for gaze cues (e.g. Frischen & Tipper, 2004; Jingling et al., 2015). In our data, facilitation occurred at the expected SOA of 650 ms, thereby replicating previous findings (e.g. Fischer et al., 2003). IOR followed facilitation 1000 ms later, at the SOA of 1650 ms. Hence, this interval between facilitation and inhibition closely resembles the interval described for arrow cues. However, it is much shorter than what is reported for gaze cues. Frischen and Tipper (2004) propose that IOR is observed so late with gaze cues because gaze is a socially very powerful cue potentially signalling important events in the environment. Consequently participants are reluctant to withdraw attention from the gazed-at location. In digits, this should not be a factor. The observation that IOR takes significantly longer in automated symbolic orienting to occur as compared to exogenous orienting, points to the involvement of higher order/top-down processes in IOR with central cues. A previous study by Okamoto and colleagues (Okamoto-Barth & Kawai, 2006) already hinted at the involvement of higher order processes in IOR using central non-predictive gaze cues. In their study, IOR only occurred when a high number of catch trials (33%) were included. Future studies will need to explore this hypothesis.

The fundamental question how the spatial nature of digits arises is currently addressed with two contrasting theories. On the one hand, digits are intrinsically spatial according to the mental number line hypothesis (Hubbard et al., 2005). It is proposed that attention is being moved along the internal mental number line representation as a function of the magnitude of numbers (Fischer et al., 2003; Zorzi, Priftis, & Umilta, 2002). Our finding that attentional SNARC effects are limited to digits supports the cardinal origins of the visuo-spatial attention shifts associated with numerals. This account does indeed not expect SNARC-like effects for other ordered series, such as letters (Dehaene et al., 1993). Alternatively our results are also compatible with the working memory account of number–space interactions, which proposes that serial positions of (any) stimuli are spontaneously encoded in working memory and associated to a left/right polarity during task execution (Abrahamse, van Dijck, Majerus, & Fias, 2014; van Dijck & Fias, 2011; van Dijck et al., 2014). Furthermore the findings of van Dijck and colleagues (van Dijck et al., 2013) have indicated that serial-order WM is directly linked to spatial attention in the way that retrieval of early/ late items of a series from WM induces left-ward/right-ward shifts of spatial attention respectively (van Dijck et al., 2013). Since the ordinal aspect of letters (i.e. position in the alphabet) is not a core property of their semantic meaning, letter ordinality might not be accessed automatically in a target detection task. The observation that digits but not letters oriented visuo-spatial attention could therefore also result from failure to automatically access ordinal information in letters contrary to numbers, when they are passively viewed as uninformative attentional cues. This proposal is supported by the fact that recent attentional SNARC studies exclusively found attentional orienting effects (i.e. facilitation at short SOAs) when the order of non-numerical stimuli (e.g. letters) was task-relevant (Dodd et al., 2008) or stored in working memory (van Dijck et al., 2014). In contrast, attentional facilitation effects were restricted to digits (excluding letters, days of the week and calendar months) when the central cues were viewed passively3 (see also Casarotti, Michielin, Zorzi, & Umilta, 2007; Zorzi, Priftis, Meneghello, Marenzi, & Umilta, 2006).

3 In traditional SNARC studies, which always require active processing of the SNARCstimuli, order-space associations verify for both order-relevant and order-irrelevant tasks and have been observed using over-learned, non-numerical sequences such as calendar months, days of the week and letters of the alphabet (Gevers et al., 2003; Gevers, Reynvoet, & Fias, 2004), as well as newly learned sequences of words and images (Previtali, de Hevia, & Girelli, 2010).

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Future studies should investigate to what degree facilitation and IOR effects can be obtained with non-numerical ordinal stimuli like letters or weekdays, when the order is task-relevant or stored in working memory. It might for instance be argued that stimulus-order is primed by task instructions in order-relevant attentional SNARC tasks (see Dodd et al., 2008), resulting in order–space interactions with nonnumerical ordinal cues (for a review see also Fias, Van Dijck, & Gevers, 2011). On the other hand spontaneous ordering of non-numerical stimuli might be too weak and inconsistent to yield significant attentional orienting effects in tasks that simply require passive viewing of central spatially uninformative cues. Investigating potential IOR effect using the working memory based paradigm of van Dijck et al. (2014) might thus be another lead towards understanding the mechanisms underlying attentional SNARC effects. In conclusion, we examined the visuo-spatial attention effects induced by task-irrelevant central digits and letters at different SOAs. Whereas initial response facilitation was followed by IOR after passively viewing Arabic digits, no such shifts were observed when using letters as central cues. These data further qualify numerals as central symbolic cues inducing automated symbolic orienting effects (Ristic & Kingstone, 2012), hence unintentionally shifting visuo-spatial attention, even when they are spatially uninformative and task-irrelevant. Acknowledgements This work was funded by the University of Luxembourg (F3R-EMAPUL-09NSP2) and the National Research Fund (AFR PHD-09-160), Luxembourg. References Abrahamse, E. L., van Dijck, J. P., Majerus, S., & Fias, W. (2014). Finding the answer in space: The mental whiteboard hypothesis on serial order in working memory. Frontiers in Human Neuroscience, 8, 932. http://dx.doi.org/10.3389/fnhum.2014. 00932. Berlucchi, G. (2006). Inhibition of return: A phenomenon in search of a mechanism and a better name. Cognitive Neuropsychology, 23(7), 1065–1074. Casarotti, M., Michielin, M., Zorzi, M., & Umilta, C. (2007). Temporal order judgment reveals how number magnitude affects visuospatial attention. Cognition, 102(1), 101–117. Chica, A. B., & Lupiáñez, J. (2009). Effects of endogenous and exogenous attention on visual processing: An inhibition of return study. Brain Research, 1278, 75–85. Chica, A. B., Klein, R. M., Rafal, R. D., & Hopfinger, J. B. (2010). Endogenous saccade preparation does not produce inhibition of return: Failure to replicate Rafal, Calabresi, Brennan, & Sciolto (1989). Journal of Experimental Psychology: Human Perception and Performance, 36(5), 1193–1206. Chica, A. B., Lupiáñez, J., & Bartolomeo, P. (2006). Dissociating inhibition of return from endogenous orienting of spatial attention: Evidence from detection and discrimination tasks. Cognitive Neuropsychology, 23(7), 1015–1034. de Hevia, M. D., Vallar, G., & Girelli, L. (2008). Visualizing numbers in the mind's eye: The role of visuo-spatial processes in numerical abilities. Neuroscience and Biobehavioral Reviews, 32(8), 1361–1372. Dehaene, S. (1992). Varieties of numerical abilities. Cognition, 44(1–2), 1–42. Dehaene, S., Bossini, S., & Giraux, P. (1993). The mental representation of parity and number magnitude. Journal of Experimental Psychology: General, 122(3), 371–396. Dodd, M. D., & Wilson, D. (2009). Training attention: Interactions between central cues and reflexive attention. Visual Cognition, 17(5), 736–754. Dodd, M. D., Van der Stigchel, S., Adil Leghari, M., Fung, G., & Kingstone, A. (2008). Attentional snarc: There's something special about numbers (let us count the ways). Cognition, 108(3), 810–818. Driver, J., Davis, G., Ricciardelli, P., Kidd, P., Maxwell, E., & Baron-Cohen, S. (1999). Gaze perception triggers reflexive visuospatial orienting. Visual Cognition, 6(5), 509–540. Fias, W., & Fischer, M. H. (2005). Spatial representation of numbers. In J. I. D. Campbell (Ed.), Handbook of mathematical cognition. New York: Psychology Press. Fias, W., Brysbaert, M., Geypens, F., & d'Ydewalle, G. (1996). The importance of magnitude information in numerical processing: Evidence from the SNARC effect. Mathematical Cognition, 2, 95–110. Fias, W., Van Dijck, J. P., & Gevers, W. (2011). How number is associated with space? The role of working memory. In S. Dehaene, & E. Brannon (Eds.), Space, time and number in the brain: Searching for the foundations of mathematical thought, Vol. 24, Elsevier. Fischer, M. H., & Knops, A. (2014). Attentional cueing in numerical cognition — A Commentary on Zanolie & Pecher (2014). Frontiers in Psychology, 5, 1381. http://dx.doi. org/10.3389/fpsyg.2014.01381. Fischer, M. H., Castel, A. D., Dodd, M. D., & Pratt, J. (2003). Perceiving numbers causes spatial shifts of attention. Nature Neuroscience, 6(6), 555–556.

79

Folk, C. L., Remington, R. W., & Johnston, J. C. (1992). Involuntary covert orienting is contingent on attentional control settings. Journal of Experimental Psychology: Human Perception and Performance, 18(4), 1030–1044. Friesen, C. K., & Kingstone, A. (1998). The eyes have it! Reflexive orienting is triggered by nonpredictive gaze. Psychonomic Bulletin & Review, 5(3), 490–495. Frischen, A., & Tipper, S. P. (2004). Orienting attention via observed gaze shift evokes longer term inhibitory effects: Implications for social interactions, attention, and memory. Journal of Experimental Psychology: General, 133(4), 516–533. Frischen, A., Bayliss, A. P., & Tipper, S. P. (2007a). Gaze cueing of attention: Visual attention, social cognition and individual differences. Psychological Bulletin, 133(4), 694–724. Frischen, A., Smilek, J. D., & Tipper, S. P. (2007b). Inhibition of return in response to gaze cues: The roles of time course and fixation cue. Visual Cognition, 15(8), 881–895. Galfano, G., Rusconi, E., & Umilta, C. (2006). Number magnitude orients attention, but not against one's will. Psychonomic Bulletin & Review, 13(5), 869–874. Galton, F. (1880). Visualised numerals. Nature, 21, 43–74. Gevers, W., Reynvoet, B., & Fias, W. (2003). The mental representation of ordinal sequences is spatially organized. Cognition, 87, B87–B95. Gevers, W., Reynvoet, B., & Fias, W. (2004). The mental representation of ordinal sequences is spatially organized: Evidence from days of the week. Cortex, 40(1), 171–172. Gibson, B. S., & Kingstone, A. (2006). Visual attention and the semantics of space: Beyond central and peripheral cues. Psychological Science, 17(7), 622–627. Goffaux, V., Martin, R., Dormal, G., Goebel, R., & Schiltz, C. (2012). Attentional shifts induced by uninformative number symbols modulate neural activity in human occipital cortex. Neuropsychologia, 50(14), 3419–3428. Hommel, B., Pratt, J., Colzato, L., & Godijn, R. (2001). Symbolic control of visual attention. Psychological Science, 12(5), 360–365. Hubbard, E. M., Piazza, M., Pinel, P., & Dehaene, S. (2005). Interactions between number and space in parietal cortex. Nature Reviews Neuroscience, 6(6), 435–448. Hubbard, E. M., Ranzini, M., Piazza, M., & Dehaene, S. (2009). What information is critical to elicit interference in number–form synaesthesia? Cortex, 45(10), 1200–1216. James, W. (1890). The principles of psychology, Vol. 1, New York: Henry Holt & Co. Jarick, M., Dixon, M. J., Maxwell, E. C., Nicholls, M. E., & Smilek, D. (2009). The ups and downs (and lefts and rights) of synaesthetic number forms: Validation from spatial cueing and SNARC-type tasks. Cortex, 45(10), 1190–1199. Jingling, L., Lin, H. -F., Tsai, C. -J., & Lin, C. -C. (2015). Development of inhibition of return for eye gaze in adolescents. Journal of Experimental Child Psychology, 137, 76–84. Jonides, J. (1981). Voluntary versus automatic control over the mind's eye's movement, Vol. IX, Hillsdale, NJ: Lawrence Erlbaum and Associates. Klein, R. M. (2000). Inhibition of return. Trends in Cognitive Sciences, 4(4), 138–147. Langton, S. R., & Bruce, V. (1999). Reflexive visual orienting in response to the social attention of others. Visual Cognition, 6(5), 541–567. Langton, S. R., & Bruce, V. (2000). You must see the point: Automatic processing of cues to the direction of social attention. Journal of Experimental Psychology: Human Perception and Performance, 26(2), 747–757. Lorch, R. F., Jr., & Myers, J. L. (1990). Regression analyses of repeated measures data in cognitive research. Journal of Experimental Psychology: Learning, Memory, and Cognition, 16(1), 149–157. Lupiáñez, J., Decaix, C., Sieroff, E., Chokron, S., Milliken, B., & Bartolomeo, P. (2004). Independent effects of endogenous and exogenous spatial cueing: Inhibition of return at endogenously attended target locations. Experimental Brain Research, 159(4), 447–457. Lupiáñez, J., Martín-Arévalo, E., & Chica, A. B. (2013). Is Inhibition of Return due to attentional disengagement or to a detection cost? The Detection Cost Theory of IOR. Psicológica, 34, 221–252. Marotta, A., Pasini, A., Ruggiero, S., Maccari, L., Rosa, C., Lupiáñez, J., & Casagrande, M. (2013). Inhibition of return in response to eye gaze and peripheral cues in young people with Asperger's syndrome. Journal of Autism and Developmental Disorders, 43(4), 917–923. Mathôt, S., & Theeuwes, J. (2010). Gradual remapping results in early retinotopic and late spatiotopic inhibition of return. Psychological Science, 21(12), 1793–1798. Moyer, R. S., & Landauer, T. K. (1967). Time required for judgements of numerical inequality. Nature, 215(5109), 1519–1520. Okamoto-Barth, S., & Kawai, N. (2006). The role of attention in the facilitation effect and another “inhibition of return”. Cognition, 101(3), B42–B50. Posner, M. I. (1980). Orienting of attention. The Quarterly Journal of Experimental Psychology, 32(1), 3–25. Posner, M. I., & Cohen, Y. (1984). Components of visual orienting, Vol. X, Hillsdale, NJ: Lawrence Erlbaum and Associates. Posner, M. I., Rafal, R. D., Choate, L. S., & Vaughan, J. (1985). Inhibition of return: Neural basis and function. Cognitive Neuropsychology, 2(3), 211–228. Pratt, J., & Hommel, B. (2003). Symbolic control of visual attention: The role of working memory and attentional control settings. Journal of Experimental Psychology: Human Perception and Performance, 29(5), 835–845. Previtali, P., de Hevia, M. D., & Girelli, L. (2010). Placing order in space: The SNARC effect in serial learning. Experimental Brain Research, 201(3), 599–605. Price, M. C., & Mattingley, J. B. (2013). Automaticity in sequence-space synaesthesia: A critical appraisal of the evidence. Cortex, 49(5), 1165–1186. Rafal, R. D., Calabresi, P. A., Brennan, C. W., & Sciolto, T. K. (1989). Saccade preparation inhibits reorienting to recently attended locations. Journal of Experimental Psychology: Human Perception and Performance, 15(4), 673–685. Ranzini, M., Dehaene, S., Piazza, M., & Hubbard, E. M. (2009). Neural mechanisms of attentional shifts due to irrelevant spatial and numerical cues. Neuropsychologia, 47(12), 2615–2624.

80

D. Hoffmann et al. / Acta Psychologica 163 (2016) 74–80

Restle, F. (1970). Speed of adding and comparing numbers. Journal of Experimental Psychology, 91, 191–205. Ristic, J., & Kingstone, A. (2006). Attention to arrows: Pointing to a new direction. The Quarterly Journal of Experimental Psychology, 59(11), 1921–1930. Ristic, J., & Kingstone, A. (2009). Rethinking attentional development: Reflexive and volitional orienting in children and adults. Developmental Science, 12(2), 289–296. Ristic, J., & Kingstone, A. (2012). A new form of human spatial attention: Automated symbolic orienting. Visual Cognition, 20(3), 244–264. Ristic, J., Friesen, C. K., & Kingstone, A. (2002). Are eyes special? It depends on how you look at it. Psychonomic Bulletin & Review, 9(3), 507–513. Ristic, J., Landry, M., & Kingstone, A. (2012). Automated symbolic orienting: The missing link. Frontiers in Psychology, 3, 560. Ristic, J., Wright, A., & Kingstone, A. (2006). The number line effect reflects top-down control. Psychonomic Bulletin & Review, 13(5), 862–868. Ristic, J., Wright, A., & Kingstone, A. (2007). Attentional control and reflexive orienting to gaze and arrow cues. Psychonomic Bulletin & Review, 14(5), 964–969. Ruz, M., & Lupiáñez, J. (2002). A review of attentional capture: On its automaticity and sensitivity to endogenous control. Psicológica, 23, 283–309. Salillas, E., El Yagoubi, R., & Semenza, C. (2008). Sensory and cognitive processes of shifts of spatial attention induced by numbers: An ERP study. Cortex, 44(4), 406–413. Schneider, W., Eschmann, A., & Zuccolotto, A. (2002). E-prime user's guide. Pittsburgh: Psychology Software Tools Inc. Schuller, A. -M., Hoffmann, D., Goffaux, V., & Schiltz, C. (2014). Shifts of spatial attention cued by irrelevant numbers: Electrophysiological evidence from a target discrimination task. Journal of Cognitive Psychology. http://dx.doi.org/10.1080/20445911.2014. 946419. Tang, J., Ward, J., & Butterworth, B. (2008). Number forms in the brain. Journal of Cognitive Neuroscience, 20(9), 1547–1556.

Taylor, T. L., & Klein, R. M. (2000). Visual and motor effects in inhibition of return. Journal of Experimental Psychology: Human Perception and Performance, 26(5), 1639–1656. Tipples, J. (2002). Eye gaze is not unique: Automatic orienting in response to uninformative arrows. Psychonomic Bulletin & Review, 9(2), 314–318. van Dijck, J. P., & Fias, W. (2011). A working memory account for spatial–numerical associations. Cognition, 119(1), 114–119. van Dijck, J. P., Abrahamse, E. L., Acar, F., Ketels, B., & Fias, W. (2014). A working memory account of the interaction between numbers and spatial attention. The Quarterly Journal of Experimental Psychology, 67(8), 1500–1513. van Dijck, J. P., Abrahamse, E. L., Majerus, S., & Fias, W. (2013). Spatial attention interacts with serial-order retrieval from verbal working memory. Psychological Science, 24(9), 1854–1859. van Galen, M. S., & Reitsma, P. (2008). Developing access to number magnitude: A study of the SNARC effect in 7- to 9-year-olds. Journal of Experimental Child Psychology, 101(2), 99–113. Warner, C. B., Juola, J. F., & Koshino, H. (1990). Voluntary allocation versus automatic capture of visual attention. Perception & Psychophysics, 48(3), 243–251. Wood, G., & Fischer, M. H. (2008). Numbers, space, and action — from finger counting to the mental number line and beyond. Cortex, 44(4), 353–358. Yantis, S., & Jonides, J. (1984). Abrupt visual onsets and selective attention: Evidence from visual search. Journal of Experimental Psychology: Human Perception and Performance, 10(5), 601–621. Zanolie, K., & Pecher, D. (2014). Number-induced shifts in spatial attention: A replication study. Frontiers in Psychology, 5, 987. http://dx.doi.org/10.3389/fpsyg.2014.00987. Zorzi, M., Priftis, K., Meneghello, F., Marenzi, R., & Umilta, C. (2006). The spatial representation of numerical and non-numerical sequences: Evidence from neglect. Neuropsychologia, 44(7), 1061–1067. Zorzi, M., Priftis, K., & Umilta, C. (2002). Brain damage: Neglect disrupts the mental number line. Nature, 417(6885), 138–139.