Phonological facilitation in picture naming: When and where? A tDCS study

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7 April 2017 Please cite this article in press as: Pisoni A et al. Phonological facilitation in picture naming: When and where? A tdcs study. neuroscience (2017), http:// dx.doi.org/10.1016/j.neuroscience.2017.03.043 1

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PHONOLOGICAL FACILITATION IN PICTURE NAMING: WHEN AND WHERE? A tDCS STUDY

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ALBERTO PISONI, a,b* MILENA CERCIELLO, a ZAIRA CATTANEO a,c AND COSTANZA PAPAGNO a,b

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a

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Department of Psychology, Universita` degli studi di Milano Bicocca, P.zza Dell’Ateneo Nuovo 1, 20126 Milano, Italy

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b

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c

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NeuroMi, Milan Center for Neuroscience, Milano, Italy

Brain Connectivity Center, National Neurological Institute C. Mondino, Pavia, Italy

Abstract—Phonological facilitation (PF) refers to a reduction of naming latencies when a phonologically related word is presented concurrently with the target picture, as compared to the presentation of phonologically unrelated words. According to spread of activation models of word production, this effect arises after lexical selection, during phonetic encoding, and is due to the co-activation of the phonemes shared by the target word and the distracter. Conversely, semantic interference (SI) is characterized by longer naming latencies when semantically related distracters are concurrently presented with the target picture. This effect seems to arise before lexical selection. However, alternative hypotheses postulate that PF and SI both arise at a post lexical level. In this study, we aim to shed light on this debate by investigating the neural correlates of the PF and by comparing these results with those of previous studies on SI. In two experiments, we applied anodal transcranial direct current stimulation (tDCS) over the left superior temporal gyrus (LSTG) and left inferior frontal gyrus (LIFG) before a picture-word interference task in which auditory distracters, which could be phonologically related or unrelated, were presented at a SOA of 150 ms or 300 ms. While stimulating the LSTG significantly reduced the PF by decreasing RTs in phonologically unrelated trials, anodal tDCS over the LIFG did not affect PF. In line with previous results, our findings support the ‘‘activation by competition” model, pointing to inhibition between target and distracters nodes as the mechanism involved in the occurrence of PF and SI. Ó 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

Key words: tDCS, LSTG, LIFG, phonological facilitation, picture naming, activation by competition.

*Correspondence to: A. Pisoni, Department of Psychology, Universita` degli studi di Milano Bicocca, P.zza dell’Ateneo Nuovo 1, 20126 Milano, Italy. E-mail address: [email protected] (A. Pisoni). Abbreviations: LIFG, left inferior frontal gyrus; LSTG, left superior temporal gyrus; PF, phonological facilitation; PWI, picture-word interference; SI, semantic interference; SOAs, stimulus onset asynchronies; tDCS, transcranial direct current stimulation; TMS, Transcranial Magnetic Stimulation. http://dx.doi.org/10.1016/j.neuroscience.2017.03.043 0306-4522/Ó 2017 IBRO. Published by Elsevier Ltd. All rights reserved. 1

INTRODUCTION

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In the last decades, researchers have been significantly involved in unraveling the neural correlates of language processing (for reviews see Indefrey, 2011; Price, 2012). In particular, linguistic research and neuroscience cooperated in defining how the brain-language interface is structured, dissecting language complexity, and trying to link each sub-process with a specific cortical functional network (e.g. Friederici, 2011; Berwick et al., 2013). This interdisciplinary approach has been fruitful for both fields, helping defining the characteristics of specific stages of linguistic processes, and shedding light on how different brain structures communicate to create dynamic processing clusters. A fine-grained understanding of the neural processes is thus required to give credit to behavioral findings and possibly unravel otherwise unclear questions. Among language sub-components, single word production is one of the most studied aspects. Object naming, a key task in studying single word production, is a complex task, which requires the coordination of a series of processes, such as object recognition, lexical retrieval, phonological encoding and articulation (e.g., Levelt, 1999, 2001; Indefrey and Levelt, 2000, 2004; Indefrey, 2011). In the case of picture naming, after lemma selection (i.e. the lexical form of a word, including its semantic and grammatical features, but not the phonological or orthographic ones, cf. Badecker et al., 1995), representations in the phonological output lexicon are activated. This lexicon contains word forms as sequences of phonemes, which are retrieved as separate units and transformed into motor plans in the phonological buffer in order to correctly articulate the target word (Indefrey, 2011). Each of these stages is supported by a specific neural correlate. Briefly, the left middle and inferior frontal gyri (LMFG and LIFG, respectively), and the posterior portion of the left superior temporal gyrus (LSTG) are involved in lexical retrieval. The LSTG, the left ventral pars opercularis and left premotor cortex seem to be crucial for phonological and phonetic encoding and the prepost central regions as well as subcortical structures (putamen) for overt articulation (Indefrey, 2011; Price, 2012). This simplified summary of word production-related areas becomes more complex when language tasks are performed in combination with different context demands, which is perhaps closer to what happens in real-world interactions when language production occurs in the presence of a plurality of incoming linguistic stimuli. A peculiar case is, for example, when naming is

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required during the simultaneous presentation of distracters, as in the picture-word interference (PWI) paradigm. In this task, participants are asked to name objects while attempting to ignore words that are either visually superimposed on the object, or auditory presented (Schriefers et al., 1990; Damian and Martin, 1999; Starreveld, 2000; De Zubicaray and McMahon, 2009; Damian and Bowers, 2009). The distracters can be either related (i.e. belonging to the same semantic category or sharing part of the phonological properties) or unrelated to the target word. The presentation of a distracter should automatically trigger its processing, which according to different word production models may end at the lexical level (Roelofs, 1992, 1997; Levelt, 1999), or may as well proceed with the activation of the phonemes of the competing word (Dell, 1986; Harley, 1993; Peterson and Savoy, 1998; Rapp and Goldrick, 2000; de Zubicaray et al., 2001; Mechelli et al., 2007; De Zubicaray et al., 2009). Crucially, semantically and phonologically related distracters differently affect naming latencies. Studies with PWI paradigms and blocked naming tasks showed that picture naming is slower if accompanied by an auditory or visually presented semantically related word compared to the condition in which a semantically unrelated one is presented (the socalled ‘‘semantic interference effect”, SI; Schriefers et al., 1990; Belke et al., 2005; Costa et al., 2005; Moss et al., 2005; Pisoni et al., 2012; Schnur and Martin, 2012). Conversely, when the target is presented together with a phonologically related word, RTs are faster than with a phonologically unrelated one (e.g., Lupker, 1982; Rayner and Springer, 1986; Schriefers et al., 1990; Starreveld and La Heij, 1995, 1996; Starreveld, 2000; De Zubicaray et al., 2002; Abel et al., 2009; Damian and Bowers, 2009; De Zubicaray and McMahon, 2009). This effect is known as ‘‘phonological facilitation effect” (PF). PF has been shown in PWI paradigms with distracters presented both in the written (Lupker, 1982; Damian and Martin, 1999; De Zubicaray et al., 2002) and auditory modality (Schriefers et al., 1990; Meyer and Schriefers, 1991; Damian and Martin, 1999; Starreveld, 2000; Abel et al., 2006; De Zubicaray and McMahon, 2009). Crucially, the facilitation effect disappears at given stimulus onset asynchronies (SOAs), which differ according to the presentation modality. Namely, written distracters produce PF for SOAs ranging from 200 ms to +200 ms (Starreveld and La Heij, 1996; Damian and Martin, 1999; De Zubicaray et al., 2002), while auditory facilitators trigger greater PF from 100 ms to +200 ms SOAs (Schriefers et al., 1990; Damian and Martin, 1999; De Zubicaray and McMahon, 2009). The SI and PF effects, thus, seem in contrast to each other. Indeed, the SI increases RTs when target and distracter are close in semantic features, while the PF reduces RT when target and distracter share the initial or terminal phonemes. What differs between these two effects is the stage at which they take place: SI is the result of a competition at the lexical selection stage (Damian et al., 2001; Belke et al., 2005; Schnur et al.,

2006; Ganushchak and Schiller, 2008; Abdel Rahman and Melinger, 2011), while PF seems to act at the phonetic encoding level (Schriefers et al., 1990; Meyer and Schriefers, 1991; Roelofs, 1992; Meyer, 1996; De Zubicaray et al., 2002; De Zubicaray and McMahon, 2009), i.e. after lexical selection, when the phonemes of the target word are combined into syllables and the prosodic information is added (Roelofs, 1997; Indefrey, 2011). While SI arises when the target word has to be selected, PF occurs when lexical selection has already taken place (Dell’Acqua et al., 2007; Ayora et al., 2011). Previous studies proposed that the SI and PF effects might depend on either excitatory or inhibitory processes (see Schnur et al., 2006), both related to word production models (e.g., Roelofs, 1992, 1997; Levelt, 1999) in which the elements of each stage (semantic, lexical, phonemic) are represented as nodes forming a network whose connections are ordered from a more general to a more specific level. For example, in the semantic network concepts are organized from a more general attribute (category, e.g., ‘‘Animals”) to more specific features (specific exemplar, e.g., ‘‘Horse”). Within this framework, the excitatory explanation of the SI effect (Belke et al., 2005; see also Forde et al., 1997) implies that semantic relatedness produces an over-activation state (Forde et al., 1997) of items belonging to the same semantic category, increasing the competition between the target and its category-coordinates. In this case, naming animal pictures during the presentation of a semantically related word increases the activation in the semantic node representing the ‘‘animal” category and in the lexical concepts representing its exemplars, resulting in an increased competition among them (e.g. Pisoni et al., 2012). Regarding the PF effect, several pieces of behavioral and neuroimaging experimental evidence (Damian and Bowers, 2003, 2009; De Zubicaray and McMahon, 2009) indicate that a cascade of phonological coactivation of all the competing items is necessary in order to explain why it occurs. The co-occurrent presentation of the target and the distracter leads to the activation of the lexical and word-form level of both items (i.e. their phonetic constituents; De Zubicaray and McMahon, 2009). When the selection by competition mechanism reaches the phonetic encoding stage, two configurations of activation may occur. In the case of phonologically related distracters, the target phonemes are over-activated, receiving inputs from both the target and the distracters. In turn, when phonologically unrelated distracters are presented, both the target and the distracter phonemes are activated and, in order to select the correct ones, the interfering information has to be inhibited. The facilitation is thus induced during word-form assembly, thanks to the co-occurrent activation of overlapping phonological features of the target and the distracter words (see introduction in De Zubicaray and McMahon, 2009). Nevertheless, interactive models of word production (e.g. Dell, 1986; Dell and O’Seaghdha, 1994; Schwartz et al., 2004) do not exclude feedback from the word-form level to the lexical-conceptual level, thus leaving open the possibility that the effect arising at the phonological level might also

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affect lexical selection (De Zubicaray and McMahon, 2009; Jescheniak et al., 2014). However, the most controversial issue is how the activation of competitors is suppressed once the cascading activation has co-activated word-forms of distracters. Two possible mechanisms have been hypothesized. According to a decay-based mechanism, the selected item returns with time to its baseline level (Dell and O’Seaghdha, 1991; Levelt, 1999). In turn, according to an inhibition-based mechanism, after its selection the target suppresses its own active state and that of its competitors, ending in a down-regulation of their responsiveness (e.g., Berg and Schade, 1992; Dell and O’Seaghdha, 1994; Vitkovitch et al., 2001; Goldrick and Rapp, 2007; De Zubicaray and McMahon, 2009; Vitkovitch and Cooper, 2012). Studies investigating the neural correlates of the SI and PF effects may help in disentangling this debate. Several cortical areas are linked to the occurrence of these effects. Concerning SI, a strong candidate is the left middle temporal lobe. Indeed, this area plays an important role in semantically driven lexical retrieval (e.g., Mummery et al., 1996; Friedman et al., 1998; Moore and Price, 1999; Bell et al., 2001; De Zubicaray et al., 2001; Glosser and Donofrio, 2001; Antonucci et al., 2008). Accordingly, anodal transcranial direct current stimulation (tDCS) on this area enhanced SI, possibly increasing the competition between the target word and its semantically related distracters (Pisoni et al., 2012). In turn, the PF is likely linked to the activity of LSTG. Decreased BOLD signal in this region was reported during naming in presence of phonologically related as compared to phonologically unrelated distracters (De Zubicaray et al., 2001; Abel et al., 2009; De Zubicaray and McMahon, 2009), or in absence of any interference (De Zubicaray and McMahon, 2009). PF seems to engage also the LIFG (De Zubicaray et al., 2006; De Zubicaray and McMahon, 2009); however, De Zubicaray et al. (2009) showed that this region was active when both phonologically or semantically related distracters were presented. Similarly, other studies failed to find a specificity for the LIFG in phonological tasks, thus linking its activation to a general role in linguistic processing (Poldrack et al., 1999; McDermott et al., 2003; Gitelman et al., 2005), mainly at the stage of response selection (Thompson-Schill et al., 2005; Pisoni et al., 2012; but see Demonet et al., 1992; Zatorre and Evans, 1992; Rumsey et al., 1997 for a specific role of the LIFG in phonological vs. semantic tasks). Non-invasive transcranial stimulation techniques, which allow directly testing the causal involvement of an area in task execution, might shed light on the role of the LIFG and posterior temporal regions in PF. Specifically, concerning the role of the LIFG in phonological processing and interference during naming, a prior Transcranial Magnetic Stimulation (TMS) study showed a possible rostro-caudal dissociation in this region, with more anterior parts involved in semantic tasks and caudal ones in phonological judgements (Gough et al., 2005). Crucially, Schuhmann et al. (2012) found that TMS applied over the middle portion of LIFG affected phonological processing during naming. In other

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studies, inhibitory rTMS applied over the LIFG modulated semantic competition (Krieger-Redwood and Jefferies, 2014). Accordingly, tDCS studies found the LIFG to be involved in both phonemic and semantic fluency (Iyer et al., 2005; Cattaneo et al., 2011; Meinzer et al., 2012; Penolazzi et al., 2013). Concerning the role of the LIFG and the LSTG in SI, Pisoni et al. (2012) reported a reduced SI after LIFG and an increased SI after LSTG anodal tDCS in a blocked naming task. As regarding LIFG results, the authors interpreted the reduction in SI as an enhancement of the selection mechanism needed to resolve lexical competition. The increase in SI after LSTG stimulation, instead, was related to a modulation of the spread of activation through the lexical network. Henseler et al. (2014), at a descriptive level, highlighted an increased SI after pMTG stimulation while associative facilitation was abolished, probably depending on the same mechanism found in Pisoni et al. (2012). In contrast, LIFG stimulation did not affect SI in that study. Conversely, Wirth et al. (2011) found a reduced SI effect after LIFG stimulation, which was mirrored by a reduction of delta band oscillation in a resting state EEG acquired after tDCS. More recently, Meinzer et al. (2016) showed an involvement of the MTG and LIFG in the SI combining a blocked naming paradigm with an online a-tDCS protocol. Crucially, no stimulation study so far investigated the role of the LIFG and LSTG in PF. In the present study we aimed to address this issue by stimulating with anodal tDCS the LSTG (Experiment 1) and the LIFG (Experiment 2), before a PWI paradigm with phonologically related and unrelated distracters. We expected to define whether and how these regions are involved in PF, and, critically, to assess whether the LSTG is involved in spread of activation processes underlying activation by competition selection, or whether it underpins lateral inhibition between target and distracters’ nodes at the phonetic encoding level. In particular, since the LSTG has been reported to be specifically associated to the PF (De Zubicaray et al., 2001; Abel et al., 2009; De Zubicaray and McMahon, 2009), we expected stimulation over this area to modulate the PF. If this area is linked to spread of activation, we should observe a decrease in RTs in the phonologically related condition, since the target phonemes should be over-activated by the target, the distracter and the stimulation. We should also observe an increase in RTs in the phonologically unrelated condition, since the distracter phoneme representations would be boosted by tDCS. On the other hand, if the LSTG sub-serves lateral inhibitory processes, we should report a decrease in RTs in the phonologically unrelated condition, since competing phonemes would be more inhibited. Conversely, since LIFG activation has been observed for picture naming when both phonologically and semantically related distracters are concurrently presented, we expected anodal tDCS over this area to modulate more general processes associated with picture naming, without affecting PF per se. Moreover, by comparing the present results with the ones from a previous study from our group on SI (Pisoni et al., 2012), we will discuss the potential impact of the results on cognitive models of picture naming.

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EXPERIMENTAL PROCEDURES

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Participants

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Twelve neurologically unimpaired individuals (4 males, mean age 22 years, SD = 2.4; Range 18–25 years) took part in Experiment 1; and twelve neurologically unimpaired individuals (3 males, mean age 25 years, SD = 3.5; Range 20–30 years) who did not participate in Experiment 1, took part in Experiment 2. All participants were native Italian speakers, undergraduate students (Experiment 1: mean years of education = 13.9; SD = 1.4, range = 13–18 years; Experiment 2: mean years of education = 15.5; SD = 2.2, range = 13–18 years); they were naı¨ ve as to the experimental procedure and the purpose of the study. All subjects were right-handed (Experiment 1: mean Edinburgh handedness inventory (EHI, Oldfield, 1971) = 90; SD = 9.5; range = 79 – 100; Experiment 2: mean EHI = 95; SD = 9.8; range = 67–100), with normal or corrected-to-normal vision. They had no history of chronic or acute neurologic, psychiatric, or medical disease; no family history of epilepsy; no current pregnancy; no cardiac pacemaker; no previous surgery involving implants to the head (cochlear implants, aneurysm clips, brain electrodes) and did not take acute or chronic medication. Written informed consent was obtained from all participants. The experiment was approved by the local ethical committee of the University of Milano-Bicocca and subjects were treated in accordance with the Declaration of Helsinki.

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Stimuli

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Stimuli were 200 picture-word pairs. One hundred black and white pictures were taken from the Viggiano et al. (2004)’s inventory, a standardized set of ecological pictures for experimental and clinical research on object processing, and were divided into two experimental sets. Each set included 25 pictures of living exemplars (animals, fruits, vegetables) and 25 pictures of objects (tools, vehicles, clothing, furniture). Pictures of the two sets were matched for visual complexity and familiarity (see Appendix B Tables 1 and 2), as well as for length in letters and syllables and name frequency (this last according to the COLFIS, Bertinetto et al., 2005). Each picture appeared in two picture-word pairs, once coupled with a phonologically related and once with an unrelated word. Phonologically related distracters shared with the name of the paired picture the following features: the first 2/3 phonemes, number of letters and syllables, stress position and frequency (see Appendix A Tables A.1 and A.2). In turn, phonologically unrelated distracters were matched with the name of the associated picture only for number of syllables and letters and frequency, while initial and final phonemes and stress position differed between picture name and distracter. Distracters were read and recorded as individual ‘‘.wav” audio files. Each item set was administered in two different experimental sessions, with order of sets balanced across subjects.

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Picture-word interference task (PWI)

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The same procedure was used for the pilot and the experimental sessions. Before the experiment, pictures were randomly presented for self-paced naming, so that participants could familiarize with the stimuli and their names. Following this practice, participants were informed that after tDCS they had to name the same pictures presented in the training session as accurately and fast as possible, ignoring the concurrent auditory stimuli. Each subject performed three picture naming blocks per session. In a block, each picture appeared without any interfering word (no interference condition). In a second block, each picture-word pair was presented at a SOA of 150 ms (i.e. the auditory presented word starting 150 ms after the picture appearance), a SOA, which should induce PF. In a third block, each picture-word pair was presented at a 300 ms SOA, in which no PF should occur since the crucial timing for its appearance had elapsed (Schriefers et al., 1990; Damian and Martin, 1999; De Zubicaray and McMahon, 2009). Hence, in each naming session, every picture appeared 5 times in different contexts: no interference, with a phonologically related distracter at 150 ms or 300 ms, with a phonologically unrelated distracter at 150 ms or 300 ms, for a total of 250 naming trials. Order of blocks was counter-balanced across subjects. Each trial started with a fixation point of 500 ms followed by a blank screen (500 ms) and by the picture, lasting for 2000 ms. After the picture was shown, the audio file started at the given SOA. After naming, a fixation cross was presented (1000 ms; as in Damian and Bowers, 2009; see Fig. 1a for a timeline of an experimental trial). After each block, 1-min interval was left in order to allow participants resting before the following block. The experiment took approximately 20 min. Accuracy of correctly named items was recorded for analyses. A pilot study run on 12 subjects who did not take part in the tDCS experiments confirmed the presence of a PF effect. A repeated measures ANOVA on RTs of correct trials with SOA (2 levels: 150 and 300 ms), and type of distracter (2 levels: phonologically related vs. unrelated distracters) as within-subject variable and list (2 levels: list 1 vs. 2) as between-subject variable, highlighted a significant main effect of type of distracter [F(1,11) = 14.16; p = 0.003], since phonologically related distracters triggered faster naming latencies (593 ms) compared to phonologically unrelated distracters (624 ms), and a significant interaction SOA  type of distracter [F(1,11) = 9.8; p = 0.009]. Post-hoc analyses (Bonferroni corrected) revealed slower RTs for phonologically unrelated distracters compared to phonologically related distracters at 150 ms SOA (639 ms vs. 583 ms respectively, p = 0.003), while they did not differ at 300 ms SOA (610 ms vs. 604 ms; p = 0.43). Critically, neither the main effect of list nor any of its interactions were significant, thus confirming that both sets similarly elicited the aforementioned effects. Interestingly, as previously reported (Schriefers et al., 1990), PF effect (measured as the difference between distracters RTs and phonologically related distracters RTs) at 150 ms SOA significantly differed from PF effect at 300 ms SOA (56 ms vs. 6 ms; t(11) = 3.14; p = 0.009).

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Fig. 1. (A) Experimental timeline of the PWI paradigm. (B) Experimental timeline of the Control task. After the presentation of a fixation point for a random interval of 2200–2700 ms, one of the two frames flanking it flickered for 200 ms (Cue). Then three conditions could occur: congruent, in which a small square (target) appeared on the same side as the cue; Incongruent, when the side of the target did not match the side of the cue; Catch trial, when no target was displayed. 423

Control task

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In order to exclude an unspecific effect of tDCS on arousal, an external cueing visual paradigm (Posner paradigm, Posner and Cohen, 1984; Posner et al., 1987, 1988) was administered after the PWI experiment, including 60 trials. At the beginning of each trial, a fixation cross was presented for 2000 ms. Then, two rectangular frames appeared at the left and right of the fixation cross and, after a randomly jittering interval (200 ms-700 ms), one of the two squares blinked for 200 ms (cue). After 100 ms, a small square appeared in the center of one of the two frames (target). According to the side of the cue and target, trials could be congruent (when cue and target appeared on the same side of the screen, 24 trials), or incongruent (when cue and target appeared on the opposite side, 24 trials). Subjects had to answer where the target had appeared, as fast and accurately as they could, by pressing, with the left or right index finger, one of two aligned keys on a qwerty Italian keyboard: ‘‘F” when the target appeared to the left and ‘‘J” when it appeared to the right of the fixation point. Catch trials in which no target appeared were also included (12 trials; see Fig. 1b for a timeline of the control experiment). RTs and accuracy were collected.

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tDCS

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tDCS was delivered by a battery driven, constant current stimulator (Eldith, Neuroconn, Ilmenau, Germany) through a pair of saline-soaked sponge electrodes kept firm by elastic bands. The anode (25 cm2) was placed over the LSTG in Experiment 1, and over the LIFG in Experiment 2, while the cathode (50 cm2) was placed over the right supraorbital region. The LSTG was identified as the EEG 10–20 electrodes positioning site CP5 (Sparing et al., 2008; Fiori et al., 2010). The LIFG, instead, was identified as the crossing point between Fz-T3 Cz-F7 electrodes sites in the EEG 10–20 electrodes positioning system (Herwig et al., 2003; Cattaneo et al., 2011; Pisoni et al., 2012). Participants took part in two experimental sessions, with a break of at least 3 days in between. In real sessions, the stimulation protocol lasted for 20 min at 2 mA intensity. Current and charge densities (0.8 A/m2 and 960 C/m2 for the anode and 0.4 A/m2 and 480 C/m2 for the cathode respectively) were maintained below the safety limits (Poreisz et al., 2007). In sham sessions, the same electrodes montage as real sessions was used, but stimulation duration was only 30 s. A fade-in/out period of 30 s was administered at the beginning and at the end of the stimulation procedure. Order of stimulation condition was balanced across subjects. The study was conducted as a single-blind experiment.

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Procedure

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Subjects performed the experiment in a silent and lightened room. E-prime 2 software (Psychology Software Tools, Pittsburgh, PA) was used for the experimental procedure. A microphone triggered a voice key for RTs collection to the nearest millisecond. Before the experimental procedure, participants were instructed about the tasks and the stimulation. While stimulating, a cartoon movie with no audio was presented so that participants could relax; meanwhile, it was possible to control their visual experience during stimulation. After 18 min from the beginning of tDCS, subjects were told that they would have had to perform the experimental tasks in 2 min.

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Statistical analyses

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Data were analyzed in the statistical programing environment R (R Development Core Team, 2014). Linear mixed effects models were used as the main statistical procedure (Baayen et al., 2008). RTs of correct trials of the PWI task were submitted to a series of linear mixed effects regression using LMER procedure in ‘‘lme4” R package (version 1.1–5, Bates et al., 2014). Outliers (±3SD from the general mean) or incorrect trials were excluded from the analysis. A series of likelihood ratio tests was used to assess the inclusion of fixed effects that significantly increased the model’s goodness of fit by means of a forward stepwise inclusion procedure (Gelman and Hill, 2006). As fixed effects, Type of distracter (factorial, 2 levels: phonologically related vs. unrelated), SOA (factorial, 2 levels: 150 ms vs. 300 ms),

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Stimulation (factorial, 2 levels: real vs. sham), and their interactions were tested. Moreover, other factors that could have affected performance were controlled by testing their inclusion in the model. In particular, Experimental session (factorial, 2 levels: 1st session vs. 2nd session), Block order (factorial, 3 levels: 1st, 2nd and 3rd block), List (factorial, 2 levels: list 1 vs. list 2), Target word category (factorial, 2 levels: living vs. non-living), and, as continuous variables, pictures familiarity and complexity (as reported in Viggiano et al., 2004), target word and distracter length (in number of letters) and frequency (as reported in the ColFis) were considered. Concerning the random effect structure, a by-subject and a by-item random intercept were included. Random effect structure was determined following a forward stepwise LRT procedure, in order to identify the maximal random effect structure justified by the data (Barr et al., 2013; Matuschek et al., 2015; Bates et al., 2015a,b), by keeping the random by-subject and by-item slopes for the main effects and their interactions only when the model converged or significantly increased the model goodness of fit. We report the parameters of the final best fitting models with significance levels based on Satterthwaite’s degrees of freedom approximation in ‘‘lmerTest” R package (version 2.0–29, Kuznetsova et al., 2015). The results of the LRT procedures are reported in Appendix B Tables 1 and 2. Moreover, to directly contrast single levels of the significant interactions and main effects, post hoc procedures were carried out on the best fitting final model with the ‘‘phia” R package (version 0.2-0, De Rosario Martınez, 2015), applying Bonferroni-Holmes correction for multiple comparisons. Finally, to control whether tDCS effects involved more general naming processes, the same analysis run on RTs of trials with a distracter was run on RTs of trials in which no distracter was presented. RTs of correct trials in the control experiment were submitted to the same analysis run for RTs in the main task, considering as fix factors Type of trial (2 levels: congruent vs. incongruent), Stimulation (2 levels: real vs. sham), Cue side (2 levels: left vs. right) and Target side (2 levels: left vs. right), and adding a by subject and by trial random intercept.

RESULTS

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Experiment 1

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The final model on PWI RTs included as fixed effects the main effects of Type of distracter, SOA and Stimulation as well as Stimulation by Type of distracter and SOA by Stimulation interactions. Moreover, the main effects of Block order and target and distracters length were added. The random effect structures, instead, included the random intercept for Subjects and Target, as well as the by-subject random slope for Type of word, SOA and Stimulation and for the Stimulation by SOA interaction. The parameters of the final model concerning the main effect of Block order had a significant effect: the first block (633 ms) was in general slower than the second (580 ms, b = 41; t(11) = 3.57; p = 0.004) and the third (603 ms, b = 42; t(11) = 3.83; p = 0.003)

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ones. The parameter referring to the interaction between Stimulation and Type of distracter had a significant effect (b = 33.03); t(4.146) = 3.12; p = 0.002). In the sham condition, indeed, RTs of phonologically unrelated and related words differed (624 ms and 595 ms respectively, p = 0.018), while in the real session this difference was not significant (603 ms vs. 606 ms; p = 0.71); phonologically unrelated distracters were faster in real session compared to sham ones (p = 0.016), while phonologically related distracters were not affected by stimulation (p = 0.08; see Fig. 3). No Effect of SOA was highlighted (see Fig. 2 for naming latencies divided by SOA, Stimulation and distracter type; model parameters are reported in Table 1). Results of experiment 1 showed that enhancing LSTG activity by means of a-tDCS reduced the PF effect and that this decrement was due to a faster naming when phonologically unrelated words were presented. Hence, the present data support the evidence that LSTG is a crucial area for PF occurrence (De Zubicaray et al., 2002; Abel et al., 2009; De Zubicaray and McMahon, 2009) and, more generally, for phonological and phonetic encoding (Indefrey and Levelt, 2000). Crucially, when only sham sessions were considered, we found the PF effect (Type of word by SOA interaction: b = 28.2; t (2213) = 1.98; p = 0.048), being significant only in 150 ms SOA trials (588 ms vs. 624 ms; 300 ms SOA: 615 ms vs. 622 ms), and confirming that our paradigm was sensitive enough to detect the effect. Finally, the model run on trials without distracters showed no influence of stimulation on performance (Real: 669.2 ms; Sham: 685.1 ms; LRT: v2(1) = 2.5; p = 0.11).

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Experiment 2

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The final model run on RTs included as fixed effects the main effects of Type of distracter, SOA and Stimulation as well as the Stimulation by SOA and SOA by Type of distracter interaction. Moreover, the main effect of Session, Block order and Distracters frequency were included in the model. Random effects structures instead included a by-Subject and a by-Item random intercept, as well as a by-Subject random slope for Stimulation, SOA and their interaction and a by-Item random slope for SOA, Type of distracter and their interaction. The model showed a significant effect of Stimulation (b = 59; t(11) = 2.4; p = 0.04): RTs in real sessions were slower than in sham ones (682 ms and 645 ms respectively; See Fig. 5). Similarly, the parameter for the main effect of Distracter type resulted significant (b = 25.3; t(95) = 2.94; p = 0.004) being phonologically related distracters associated with shorter naming latencies compared to phonologically unrelated distracters (649 ms vs. 678 ms). In addition, the parameter for the main effect of Session had a marginally significant effect (b = 22; t(7.79) = 2.2; p = 0.058), since RTs in session 1 were slower than in session 2 (682 ms vs. 646 ms). Also the parameter for the main effect of Distracters frequency was significant (b = 0.16; t(125.4) = 1.92; p = 0.055). The

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t(1025.9) = 5.1; p < 0.001), since naming latencies tended to be longer in real sessions (681 ms) than in sham ones (633 ms).

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Control task

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In Experiment 1, only 1.8% of trials were rejected, preventing the accuracy analysis. The final model on RTs of correct trials did not highlight either a significant main effect of Stimulation (LRT: v2(1) = 0.97; p = 0.32) or a significant Stimulation by Type of trial Fig. 2. Mean naming latencies (in ms) for the PWI task after LSTG anodal tDCS divided by interaction (LRT: v2(1) = 0.23; Stimulation condition (real vs. sham) and SOA (150 vs. 300 ms) for (A) phonologically unrelated p = 0.63). Conversely, the model and (B) phonologically related distracters. Error bars represent ±1 MSE. included the main effect of Type of trial and Target side as fixed effects, while as random factors, the by subject random slopes for Type of trial and Target side were included. The Type of trial parameter was significant (b = 22.9; t(1064) = 2.7; p = 0.02), with incongruent trials showing longer RTs compared to congruent ones (367.7 ms vs. 349.6 ms). For Experiment 2, only 1.6% of trials were rejected, preventing the accuracy analysis. The final model on RTs included, as fixed effects, the main effects of Type of trial and Stimulation, as well as the by subject random for Type of trial and the by item slope for stimulation. The parameter for main effect of Stimulation was significant (b = 11.8; t(91.1) = 2.03; p = 0.045), with trials in real stimulation sessions showing slower RTs compared to trials in sham sessions (349.3 ms vs. 1 ms).

Fig. 3. Mean naming latencies (in ms) for PWI in Experiment 1 showing the Stimulation by Distracter type interaction. Error bars represent ±1 MSE. Asterisks indicate significant differences.

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Stimulation by SOA interaction parameter was not significant (b = 29.8; t(10.9) = 1.37; p = 0.198; see Fig. 4 for naming latencies divided by SOA, Stimulation and distracter type; model parameters are reported in Table 2). Also for experiment 2, when only sham sessions were considered, the Stimulation by SOA interaction was significant, (b = 22; t(4422) = 2.5; p = 0.013), being the phonological facilitation effect present at 150 ms SOA only (related: 618 ms; unrelated: 650 ms; 300 ms SOA: related: 644 ms; unrelated: 650 ms). The model run on trials without distracters, highlighted an effect of tDCS on general naming abilities (b = 48.4;

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DISCUSSION

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In this study we investigated the role of LSTG and LIFG in PF by administering a PWI task, with auditory phonologically related and unrelated distracters presented at 150 and 300 ms SOAs, after an anodal tDCS protocol delivered over these two regions. Critically, the aim was to clarify whether the LSTG and the LIFG play a different role in producing the PF effect and whether different mechanisms underpinned PF and SI effects, by comparing the present results with those of previous studies. Anodal tDCS over the LSTG significantly reduced the PF effect, selectively shortening RTs of PWI trials in which a phonologically unrelated distracter was presented, while no effect was observed for phonologically related distracters. In turn, the same stimulation protocol delivered over the LIFG did not modulate the PF, while the presence of a distracter, whether phonologically related or not, slowed naming latencies. There were no effects of LSTG stimulation in a control Posner task, while stimulation of the LIFG overall slowed down RTs in the control task with no difference between congruent and incongruent conditions.

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Table 1. Parameters of the final model run on RTs of correct trials in Experiment 1 Random effects: SD Target (intercept) ID (intercept) Stimulation SOA Distracter type Stimulation: SOA Residual Residual

46.33 101.85 41.48 47.38 28.37 54.03 173 141.42

Fixed effects (Intercept) Stimulation sham vs. Real SOA 300 ms vs. 150 ms Distracter type Related vs. Unrelated Block order 2 vs. 1 Block order 3 vs. 1 Block order 3 vs. 2 Target length Distracter length Stimulation sham vs. Real: SOA 300 ms vs. 150 ms Stimulation sham vs. Real: Distracter type Related vs. Unrelated

Estimate

SE

DF

t

p

589.1 7.8 17.0 4.1 41.0 42.1 1.1 1.2 5.9 24.2 33.0

37.9 15.1 15.8 11.2 11.5 11.0 11.9 4.4 3.9 18.8 10.6

27.0 15.0 10.0 19.0 11.0 11.0 11.0 246.0 1043.0 11.0 4146.0

15.5 0.5 1.1 0.4 3.6 3.8 0.1 0.3 1.5 1.3 3.1

<0.001 0.614 0.305 0.716 0.005 0.003 0.927 0.792 0.130 0.226 0.002

Number of observations: 4288; groups: ITEM: 100; ID: 12.

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of distracters exerted by target nodes, i.e. the inhibition of the phonological features of unrelated distracters (Berg and Schade, 1992; Dell and O’Seaghdha, 1994; Vitkovitch et al., 2001; Goldrick and Rapp, 2007; De Zubicaray and McMahon, 2009) during phonetic encoding. Some interactive models of word production (e.g. Berg and Schade, 1992; Harley, 1993), indeed, include mutual inhibitory connections across and within stages to account for conflict resolution. An enhancement of this mechanism, by means of a-tDCS, might have increased inhiFig. 4. Mean naming latencies (in ms) for the PWI task after LIFG anodal tDCS divided by Stimulation condition (real vs. sham) and SOA (150 vs. 300 ms) for (A) phonologically unrelated bition when this was more needed, and (B) phonologically related distracters. Error bars represent ±1 MSE. i.e. on phonologically unrelated distracters, thus improving participants’ performance in this condition by supConcerning the role of LSTG in PF occurrence, the pressing activation of distracters present results indicate that this region is critical for word-form. Conversely, enhancing inhibition on trials phonetic encoding, since anodal tDCS over this region when phonologically related distracters were present did specifically modulated naming latencies of trials with not modulate performance, since the few unrelated comphonologically unrelated distracters. Specifically, petitors were already efficiently inhibited and did not interfollowing anodal stimulation over the LSTG, fere with the selection of the target phonemes (see phonologically unrelated distracters did not interfere with Fig. 6). picture naming, finally reducing the PF effect. If tDCS In this perspective, the role of the LSTG seems crucial affected naming in general, or attentional processes in generating this inhibition. Accordingly, previous fMRI related to inhibition of distracters information, we should evidence highlighted reduced activity in this region for have detected the same effect on both distracters types. phonologically related as compared to unrelated Critically, the selective reduction of unrelated distracter distracters in a PWI task (De Zubicaray and McMahon, influence on target picture naming supports the view 2009). that activation by competition includes a lateral inhibition Please cite this article in press as: Pisoni A et al. Phonological facilitation in picture naming: When and where? A tdcs study. neuroscience (2017), http:// dx.doi.org/10.1016/j.neuroscience.2017.03.043

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Fig. 5. Mean naming latencies (in ms) for PWI in Experiment 2 showing the main effect of Stimulation. Error bars represent ±1 MSE. Asterisks indicate.

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Our data may seem at odds with previous results from our own group (Pisoni et al., 2012), in which we found an increased SI in a blocked-naming paradigm following anodal tDCS over the LSTG. We interpreted those results as reflecting an increase of activation of non-target semantically related distracters during the lexical selection stage of picture naming (Pisoni et al., 2012). However, our para-

digm did not allow to identify the core mechanism upon which SI relied, that is a spread of activation (Forde et al., 1997; Belke et al., 2005) or rather an overinhibition process (Dell, 1986; Wilshire and McCarthy, 2002; Schnur et al., 2006; Biegler et al., 2008; see Pisoni et al., 2012), since the final output with the enhancement of both mechanisms could be similar (see e.g. Biegler et al., 2008). In the present study, we tried to clarify this issue building on the assumption that the mechanisms leading to the selection by competition are supposed to be the same at the lexical and word form levels of the network (Levelt, 1999). In Experiment 1, only phonologically unrelated distracters reduced their interference after anodal tDCS, possibly due to an increase in lateral inhibition of the distracters’ nodes at the word form level. In light of these novel findings, we suggest that the same increase in lateral inhibition may have been the critical factor in increasing SI in Pisoni et al. (2012), and that an inhibition-based mechanism might be at the basis of both the SI and PF effects. Indeed, by overinhibiting semantically related items during blocked naming, SI could have increased. What differs between SI and PF effects, instead, is the stage of the network at which PF and SI effects are located, i.e. the word form and lemma stratum, respectively (Levelt, 1999). The LSTG, thus, may be involved not only in lexical retrieval, as suggested by previous evidence using non-invasive brain stimulation (Pisoni et al., 2012; Henseler et al., 2014), but more generally in cascading activation processes involved in object naming (Indefrey and Levelt, 2000; De Zubicaray et al., 2002; De Zubicaray and McMahon, 2009).

Table 2. Parameters of the final model run on RTs of correct trials in Experiment 2 Random effects: SD Target (intercept) SOA Distracter type SOA: Distracter type ID (intercept) Stimulation SOA00 Stimulation: SOA Residual

66.47 69.49 57.84 94.28 116.58 86.01 47.16 69.19 141.42

Fixed Effects (Intercept) Stimulation sham vs. Real SOA 300 ms vs. 150 ms Distracter type Related vs. Unrelated Block order 1 vs. 2 Block order 1 vs. 3 Block order 3 vs. 2 Distracter frequency Session 1 vs. 2 Stimulation sham vs. Real: SOA 300 ms vs. 150 ms SOA 300 ms vs. 150 ms: Distracter type Related vs. Unrelated

Estimate

SE

DF

t

p

687.30 59.90 33.53 25.34 93.68 94.01 0.33 0.16 22.16 29.80 16.75

36.21 25.61 17.41 8.60 15.51 14.17 12.91 0.08 10.02 21.78 12.94

13.57 10.87 16.80 95.02 8.74 8.26 8.01 152.45 7.79 10.89 93.91

18.98 2.34 1.93 2.95 6.04 6.64 0.03 1.93 2.21 1.37 1.29

<0.001 0.039 0.071 0.004 <0.001 <0.001 0.980 0.056 0.059 0.199 0.199

Number of observations: 4313; groups: ITEM: 100; ID:12.

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Fig. 6. Schematic representation of the proposed effect of anodal tDCS over the LSTG in inhibitory processes during PWI. In sham condition, when phonologically unrelated trials are presented (panel B), inhibition cannot effectively suppress the activation of all distracting phonemes, resulting in longer naming latencies. Conversely, enhancing this mechanism by means of a-tDCS (panel D) suppresses the activation of distracter phonemes.

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However, it is worth noting that not all explanations of the SI effect rely on the activation by competition account. In contrast with this model, Mahon and colleagues (2007) proposed the so-called response exclusion hypothesis according to which target lemmas enter a single-item response buffer just before being articulated. The presentation of a distracter temporarily fills the buffer, which thus needs to be cleared before the production of the correct response. The speed at which the distracter enters and is cleared from the buffer determines the degree of interference it may exert on the target item production. In particular, the ‘‘response relevance” of the distracter, i.e. how appropriate is the distracter for the naming context given by the task (e.g. a semantic overlap with the target), may slow down the clearance process. This non-competitive model postulates two key differences from competitive

ones: first, interference arises when items are already retrieved and ready for being articulated; second, interference is solved by a verbal self-monitoring mechanism which removes distracters from the response buffer (e.g. see Dhooge and Hartsuiker, 2010, 2012). Therefore, the distracter modulation of naming latencies in this model takes place at a post-lexical level, while in activation by competition models it is a product of lexical selection mechanisms. Which of the two models may better explain these phenomena is still a matter of debate, with evidence supporting the competitive models (for recent works, see Melinger and Abdel Rahman, 2013; Farrell and Abrams, 2014; Jescheniak et al., 2014) or the non-competitive ones (Navarrete et al., 2012). Results from this study and our previous one (Pisoni et al. 2012) indicate a clear segregation between the two effects, and support the acti-

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vation by competition hypothesis rather than the response selection theory. Data from Experiment 2 further support this view. Stimulation of the LIFG, indeed, did not affect the PF magnitude. Rather, stimulating the LIFG affected all the PWI conditions in which distracters were presented. The lack of a specific effect of LIFG stimulation over the PF effect has several theoretical implications. Since this area is likely involved in lexical selection-related conflict resolution, its lack of influence on PF strengthens the hypothesis that PF arises when this process has been already accomplished. Implications of this inference are that SI and PF have clearly distinct loci of onset concerning the stages of word production, so that SI occurs before lexical selection while PF is post-lexical. Following the response exclusion theory, both effects should arise at the same stage of picture naming (and in general of word production), that is at the level of the response buffer, a post-lexical stage before articulation. Our results contradict this hypothesis. However, it is worth stressing that the blocked naming paradigm used in Pisoni et al. (2012) and the PWI paradigm used in the present work are not directly comparable. Nevertheless, Blocked naming based on phonological features is able to induce a phonological facilitation (Schnur et al., 2006), and PWI paradigms are commonly used to induce SI (e.g. Damian and Martin, 1999). The effect of LIFG stimulation on PWI RTs, that is an increase in naming latencies in all distracter conditions, might appear puzzling. Stimulation of the LIFG has been repeatedly reported to enhance verbal abilities and lexical selection (Iyer et al., 2005; Cattaneo et al., 2011; Wirth et al., 2011; Meinzer et al., 2012; Pisoni et al., 2012, 2015; Nozari and Thompson-Schill, 2014). However, this particular paradigm requires a high cognitive load, mainly for allocating attentional resources to ignore distracters information. As previously reported, indeed, when PWI paradigm is performed with auditory distracters, all distracters conditions showed longer naming latencies as compared to the no-distracter condition (De Zubicaray et al., 2009). This suggests that auditory distracters might increase the proactive attentional load, that is the process of inhibiting the production of an incorrect response (Verbruggen and Logan, 2009; Aron, 2011), resulting in longer naming latencies. With this regard, Cai et al. (2015) found an increase in proactive interference in a go-no go task, after rIFG anodal tDCS: in particular, longer RTs were reported after anodal stimulation when a go response had to be produced after one or more no-go responses, which require higher inhibitory control. Hence, it could be possible that a-tDCS over the LIFG increased the amount of proactive control and thus inhibition of the concurrent non-target answer, resulting in longer RTs. The pattern observed in the control Posner paradigm supports this hypothesis, since longer RTs were recorded after a-tDCS over the LIFG as compared to sham sessions, suggesting a general increase in cognitive control over response selection. In summary, the present data support a role of the posterior LSTG in driving the PF effect, while the LIFG seems to be involved in attentional and control

processes when distracter and target words are concurrently presented. The decrease in RTs of phonologically unrelated distracters suggests an enhanced lateral inhibition during phonetic encoding. In light of the present and previous experimental evidence with non-invasive brain stimulation techniques (Wirth et al., 2011; Pisoni et al., 2012; Henseler et al., 2014), strong support is given to the activation by competition theory to explain the PF and SI effect, and it is suggested that the same mechanisms and brain regions (namely the posterior LSTG) regulate both effects. What differs is the stage of naming at which the effects occur, the SI being located at the lemma stratum (which needs an active selection mechanism subserved by the LIFG in order to be solved), and the PF occurring at the form stratum, i.e. after lexical selection.

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APPENDIX A.

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Table A1. Experimental stimuli of List 1 Picture

Phonemes

Freq

Facilitator

Phonemes

Freq

Distracter

Phonemes

Freq

Arancia/Orange Asino/Donkey Aspirapolvere/ Vacuumer Bicicletta/Bicycle

a’ranʧa ’azino aspira’polvere

36 27 2

a’rattso ’azola astrodi’namica

16 4 2

14 29 1

104

bibljo’teka

102

fo’tɔgrafo

117

Calzino/Sock Cammello/Camel Candela/Candle Cane/Dog Caramella/Candy Carciofo/Artichoke Cavallo/Horse Cravatta/Tie Delfino/Dolphin Divano/Couch Finocchio/Fennel Forbice/Scissors Formaggio/Cheese Fungo/Mushroom Giraffa/Giraffe Gufo/Owl Lampadario/ Chandelier Lattuga/Lettuce Lumaca/Snail Mappamondo/ Globe Mattarello/Rollingpin Melanzana/Eggplant Moto/Motorcycle Orologio/Watch Orso/Bear Pecora/Sheep Pennello/Brush Peperone/Pepper Pera/Pear Pettine/Comb Pinza/Pincers Pistola/Gun Poltrona/Armchair Pomodoro/Tomato

kal’tsino kam’mello kan’dela ’kane kara’mella kar’ʧɔfo ka’vallo kra’vatta del’fino di’vano fi’nɔkkjo ’fɔrbiʧe for’madʤo ’fuNgo ʤi’raffa ’gufo lampa’darjo

12 15 61 328 23 22 251 48 28 95 9 22 79 38 3 9 7

Caldaia/Boiler Campeggio/Camping Cancello/Gate Cassa/Case Campanile/ Bell tower Cartina/Map Calore/Heat Cratere/Crater Delirio/Delirium Dimora/Dwelling Fischietto/Whistle Forfora/Dandruff Foresta/Forest Fusto/Stem Gitano/Gipsy Gusto/Taste Lamantino/Manatee

kal’daja kam’pedʤo kan’ʧello ’kassa kampa’nile kar’tina ka’lore kra’tere de’lirjo di’mɔra fi’skjetto ’forfora fo’resta ’fusto ʤi’tano ’guʃʃo laman’tino

14 13 87 226 19 21 128 6 33 62 15 9 121 13 4 17 1

Bibita/Beverage Camino/Fire place Zuccherificio/Sugar factory Fotografo/ Photographer Viscere/Bowels Baratro/Chasm Stomaco/Stomach Aula/Classroom Mammifero/Mammal Bombola/Tank Polvere/Dust Pollice/Thumb Gomito/Elbow Missile/Rocket Chiocciola/Snail Vitello/Calf Cellula/Cell Atrio/Lobby Bandolo/Clew end Alpe/Alp Batuffolo/Wad

’bibita ka’mino tsukkeri’fiʧo

biʧi’kletta

Arazzo/Tapestry Asola/Buttonhole Astrodinamica/ Astrodynamics Biblioteca/Library

’viʃʃere ’baratro ’stɔmako ’aula mam’mifero ’bombola ’polvere ’pɔlliʧe ’gomito ’missile ’kjɔtʧola vi’tello ’ʧellula ’atrjo ’bandolo ’alpe ba’tuffolo

13 13 78 225 19 21 139 36 32 70 11 17 98 22 3 12 1

lat’tuga lu’maka mappa’mondo

9 11 4

Lavagna/Blackboard Lunotto/Rear window Maggiorenne/Adult

la’vaɲɲa lu’nɔtto madʤo’renne

13 3 4

Balsamo/Balm Cappero/Caper Carambola/Carom

’balsamo ’kappero ka’rambola

12 9 3

matta’rello

2

Madreperla/Nacre

madre’perla

4

Ecchimosi/Bruise

ek’kimozi

4

melan’dzana

13

Memoriale/Memorial

memo’rjale

24

Pantofola/Slipper

pan’tɔfola

14

’mɔto oro’lɔʤo ’orso ’pekora pen’nello pepe’rone ’pera ’pettine ’pintsa pi’stɔla pol’trona pomo’dɔro

187 143 69 56 29 27 43 20 13 250 168 88

Mossa/Move Orizzonte/Horizon Orma/Footprint Pentola/Pot Pendenza/Slope Pescatore/F isherman Pelo/Hair Petalo/Petal Pino/Pine tree Pilota/Pilot Portiere/Janitor Portafoglio/Wallet

’mɔssa orid’dzonte ’orma ’pentola pen’dentsa peska’tore ’pelo ’petalo ’pino pi’lɔta por’tjere porta’fɔʎʎo

108 97 25 54 17 82 86 28 35 226 133 60

’alba ve’ikolo ’uʃʃo fon’tana ’ʧɔtola ʤo’kattolo ’ɔsso sal’mone ’aNka ’kɔdiʧe ’ɔrgano de’pɔzito

144 121 21 40 24 69 102 21 11 245 164 87

Pulcino/Chick Rinoceronte/ Rhinoceros Rosa/Rose Sedia/Chair Serpente/Snake Spazzolino/ Toothbrush Tazzina/Cup Televisore/ Television-set Torta/Cake Ventilatore/Fan Volpe/Fox Zebra/Zebra

pul’ʧino rinoʧe’ronte

8 7

pul’sione ristora’tore

11 9

’alluʧe diri’ʤibile

8 10

’rɔza ’sedja ser’pente spattso’lino

197 122 53 5

Pulsione/Drive Ristoratore/Restaurant owner Rocce/Rocks Serbo/Serbian Sermone/Sermon Spaccatura/Rift

Alba/Dawn Veicolo/Vehicle Uscio/Door Fontana/Fountain Ciotola/Bowl Giocattolo/Toy Osso/Bone Salmone/Salmon Anca/Hip Codice/Code Organo/Organ Deposito/ Warehouse Alluce/Big toe Dirigibile/Airship

’rɔtʧe ’serbo ser’mɔne spakka’tura

102 106 97 18

Asta/Pole Album/Album Fulmine/Lightning Allodola/Skylark

’asta ’album ’fulmine al’lɔdola

105 113 57 7

tat’tsina televi’zore

13 49

tar’tufo tempera’mento

18 30

9 42

67 10 23 1

’tɔrʧa veteri’narjo ’volgo ’dzenit

21 21 10 2

Cintola/Waist Arcivescovo/ Archbishop Esca/Bait Pianerottolo/Landing Ascia/Axe Urbe/City

’ʧintola arʧi’veskovo

’tɔrta ventila’tore ’volpe ’dzebra

Tartufo/Truffle Temperamento/ Temper Torcia/Flashlight Veterinario/ Veterinary Volgo/Folks Zenit/Zenit

’eska pjane’rɔttolo ’aʃʃa ’urbe

27 13 21 5

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A. Pisoni et al. / Neuroscience xxx (2017) xxx–xxx Table A2. Experimental stimuli of List 2 Picture

Phonemes

Freq

Facilitator

Phonemes

Freq

Distracter

Phonemes

Freq

Albicocca/Apricot Ananas/Pineapple Banana/Banana Bicchiere/Glass Binocolo/ Binoculars Cacciavite/ Screwdriver Canarino/Canary Canguro/ Kangaroo Cappello/Hat Carota/Carrot Chitarra/Guitar Ciliegia/Cherry Cipolla/Onion Coltello/Knife Coniglio/Rabbit Cuscino/Pillow Elefante/Elephant Falce/Sickle Farfalla/Butterfly Forchetta/Fork Gallina/Hen Lampadina/Bulb Lavatrice/Washing machine Leone/Lion Libreria/ Bookcase Limone/Lemon Maiale/Pig Martello/ Hammer Mela/Apple Mucca/Cow Pantaloni/ Trousers

albi’kɔkka ’ananas ba’nana bik’kjere bi’nɔkolo katʧa’vite kana’rino kan’guro kap’pello ka’rɔta ki’tarra ʧi’ljeʤa ʧi’polla kol’tello ko’niʎʎo kuʃ’ʃino ele’fante falʧe far’falla for’ketta gal’lina lampa’dina lava’triʧe

15 15 24 162 18 5 10 12 112 41 46 14 76 117 30 57 60 8 55 25 32 24 11

Algerino/Algerian Anatra/Duck Bagnino/Lifeguard Biglietto/Ticket Bicipite/Biceps Caciarone/Talkative Caffettiera/Coffeepot Cancrena/Gangrene Capriccio/Whim Carbone/Coal Chirurgo/Surgeon Cinture/Belt Cinese/Chinese Collina/Hill Coperta/Blanket Custode/Guardian Elettori/Voter Falda/Layer Fardello/Burden Fortino/Blockhouse Galere/Jail Lamentela/Complaint Labirinto/Maze

alʤe’rino ’anatra ba’ɲɲino biʎ’ʎetto bi’ʧipite kaʧa’rone kaffet’tjera kan’krena ka’pritʧo kar’bone ki’rurgo ʧin’ture ʧi’neze kol’lina ko’perta ku’stɔde elet’tori ’falda far’dello for’tino ga’lere lamen’tela labi’rinto

10 46 18 190 5 1 5 14 56 42 51 58 51 126 74 64 138 15 11 13 81 23 27

ʧi’tɔfono ka’stigo ’kimiko mo’neta akkwe’dotto kwa’rezima ma’trikola ’pɔlline ’tsukkero ’ɔrbita ’bambola ʃ’ʃɔpero ’sintezi ’favola ’disputa serje’ta os’siʤeno ra’gu ’prɔfugo ’mandorla ’prɔɲɲozi pneu’matiko a’strɔnomo

10 13 20 170 17 4 11 12 120 38 46 100 81 121 29 51 65 3 56 27 34 32 11

le’one libre’ria li’mone ma’jale mar’tello ’mela ’mukka panta’loni

78 90 103 40 26 66 12 127

leg’genda libe’rale li’ʧentsa ma’lato mar’mitta ’meno ’muzo pano’rama

107 66 85 123 19 11 6 77

pro’filo de’pɔzito ’ʧirkolo ’kimika ’palpebra ’aʤo so’fa fi’lɔzofo

107 87 89 39 25 57 11 123

Pappagallo/Parrot Patata/Potato Penna/Pen Piccione/Pigeon Pinguino/ Penguin Piselli/Peas Ragno/Spider Scala/Stair Scarpa/Shoe Scopa/Broom Spazzola/Hair-brush Stivale/Boot Sveglia/Alarm clock Tavolo/Table Topo/Mouse Trapano/Drill Trattore/Tractor

pappa’gallo pa’tata pe’nna pit’ʧone pin’gwino pi’sello ’raɲɲo ’skala ’skarpa ’skopa ’spattsola sti’vale ’zveʎʎa ’tavolo ’tɔpo ’tra’pano trat’tore

12 99 80 19 5 14 27 217 195 12 18 44 16 390 69 9 5

papil’lɔma pa’rere ’pepe pik’kɔttsa pin’tsetta pi’lastro ’rame ’skambjo ’skatto ’skɔʎʎo ’spazimo sti’pendjo ’zvista ’tattika ’tɔrti ’tramite tra’kɔlla

4 164 102 2 2 18 23 190 79 30 7 131 7 48 85 17 3

Accumulo/Backlog Complice/Accomplice Virtu`/Virtue Zattera/Raft Ciondolo/Pendant Lealta`/Loyalty Tribu`/Tribe Treno/Train Taglio/Cut Metro`/Subway Bollino/Sticker Monaco/Monk Ambra/Amber Carcere/Jail Bonta`/ Kindness Zitella/Spinster Dondolo/ Rocking chair

ak’kumulo ’kɔmpliʧe vir’tu ’dzattera ’ʧondolo leal’ta tri’bu ’treno ’taʎʎo met’ro bol’lino ’mɔnako ’ambra ’karʧere bon’ta dzi’tella ’dondolo

10 98 80 15 6 24 33 230 174 23 18 44 8 412 50 7 7

Valigia/Suitcase Zucchina/Courgette

va’liʤa tsuk’kina

101 26

Leggenda/Legend Liberale/Liberal Licenza/Permit Malato/Sick Marmitta/Silencer Meno/Minus Muso/Muzzle Panorama/ Landscape Papilloma/Papilloma Parere/Advice Pepe/Pepper Piccozza/Mattlock Pinzetta/Tweezers Pilastro/Pillar Rame/Copper Scambio/Exchange Scatto/Sprint Scoglio/Reef Spasimo/Spasm Stipendio/Salary Svista/Blunder Tattica/Tactics Torti/Wrongs Tramite/Medium Tracolla/Shoulder belt Vapore/Steam Zuppiera/Tureen

Citofono/ Interphone Castigo/ Punishment Chimico/Chemical Moneta/Coin Acquedotto/ Aqueduct Quaresima/Lent Matricola/Fresher Polline/Pollen Zucchero/Sugar Orbita/Orbit Bambola/Doll Sciopero/Strike Sintesi/Synthesis Favola/Fairy tale Disputa/Quarrel Serieta`/Seriousness Ossigeno/Oxigen Ragu`/Ragout Profugo/Refugee Mandorla/Almond Prognosi/Prognosis Pneumatico/Tire Astronomo/ Astronomer Profilo/Profile Deposito/Deposit Circolo/Circle Chimica/Chemistry Palpebra/Eyelid Agio/Cosiness Sofa/Couch Filosofo/ Philosopher

va’pore tsup’pjera

54 5

Farmaco/Drug Briciola/Crumb

’farmako ’briʧola

143 22

Please cite this article in press as: Pisoni A et al. Phonological facilitation in picture naming: When and where? A tdcs study. neuroscience (2017), http:// dx.doi.org/10.1016/j.neuroscience.2017.03.043

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No. of Pages 16

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APPENDIX B.

1214

Table B1. LRT model selection for Experiment 1. LRT procedures were carried out by the ‘‘anova” function in lme4 R package, by comparing the model with and without the considered parameter. One parameter at a time was added in the more complex model to test its significance against the model without it. NC = Not Converging, i.e. the program could not estimate the model parameters

Table B2. LRT model selection for Experiment 2. LRT procedures were carried out by the ‘‘anova” function in lme4 R package, by comparing the model with and without the considered parameter. One parameter at a time was added in the more complex model to test its significance against the model without it. NC = Not Converging, i.e. the program could not estimate the model parameters

Fixed effects

DF

v2

p

Fixed effects

DF

v2

p

Type of word Stimulation SOA Type of word*Stimulation Type of word*SOA Stimulation*SOA Type of word*Stimulation*SOA Session Block order List Target word category Picture familiarity Picture complexity Target length Distracter length Target frequency Distracter frequency

1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1

3.9 0.42 1.11 8.83 3 4.25 0.04 0.25 58.21 0.14 2.19 0.03 0.013 4.42 5.7 3.3 1

0.48 0.52 0.29 0.003 0.08 0.04 0.84 0.62 <.001 0.71 0.14 0.85 0.91 0.03 0.017 0.8 0.31

Type of word Stimulation SOA Type of word*Stimulation Type of word*SOA Stimulation*SOA Type of word*Stimulation*SOA Session Block order List Target word category Picture familiarity Picture complexity Target length Distracter length Target frequency Distracter frequency

1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1

11.7 79.2 8.6 0.86 3.57 9.18 0.2 26.4 149.9 0.05 3.35 0.24 0.01 3.36 2.8 0.9 5.12

<0.001 <0.001 0.003 0.35 0.06 0.002 0.66 <0.001 <0.001 0.82 0.07 0.88 0.93 0.07 0.085 0.34 0.024

0.14 <.001 0.003 0.5 0.004

Random effects ID Type of word Stimulation SOA Type of word*SOA Stimulation*SOA

3 2 3 NC 4

1.9 109.8 41.7

0.59 <0.001 <0.001

37.1

<0.001

Target Type of word Stimulation SOA Type of word*SOA Stimulation*SOA

2 2 3 4 6

23.23 2.29 9.28 45.44 4.59

<0.001 0.32 0.03 <0.001 0.6

Random effects ID Type of word Stimulation SOA Type of word*Stimulation Stimulation*SOA

3 2 4 5 5

Target Type of word Stimulation SOA Type of word*Stimulation Stimulation*SOA

NC 2 2 NC NC

10.67 33.33 15.66 4.35 17.08

1.26 0.41

0.53 0.81

1215 1216 1217 1218

(Received 23 August 2016, Accepted 25 March 2017) (Available online xxxx)

Please cite this article in press as: Pisoni A et al. Phonological facilitation in picture naming: When and where? A tdcs study. neuroscience (2017), http:// dx.doi.org/10.1016/j.neuroscience.2017.03.043