A substantial body of evidence has revealed that complex words undergo an early, blind, and automatic segmentation into their constituent parts (Rastle et al., 2004; Longtin and Meunier, 2005; Marslen-Wilson et al., 2008; McCormick et al., 2008; Rastle and Davis, 2008). This process of bottom-up, stimulus-driven word segmentation highlights the critical role of morphological structure in lexical access, whereby written word forms are automatically broken down into meaningful subunits, even when these subunits are not compatible with the meaning of the whole form (e.g., corner is not someone who corns). Thus, farmer facilitates the recognition of farm, witness facilitates the recognition of wit, but spinach does not facilitate the recognition of spin since the final letters (-ach) do not form a meaningful suffix in English. At a later processing stage, however, only farmer still facilitates the recognition of farm (but witness does not facilitate wit), suggesting that only semantically transparent words, such as farmer retain morphemic structure at the level of central lexical representations (Marslen-Wilson et al., 1994).

The point at which lexical semantics begins to exert influence on morphological processing is still a matter of debate. According to the form-before-meaning account, morpho-semantic properties of complex words determine the organization of central lexical representations, but not the process of lexical access (Marslen-Wilson et al., 1994; Rastle et al., 2000; Meunier and Longtin, 2007). Recent evidence has further supported the claim that semantics does not play a role in early morpho-orthographic processing, given that blind segmentation is triggered for opaque forms even when the suffix conveys no regular meaning (e.g., -er in ponder; Beyersmann et al., 2016). Only later stages of word recognition are argued to be semantically driven, when the meaning of the whole form is accessible, and makes the interpretation of witness as containing a stem wit and suffix -ness invalid. This is supported by evidence from paradigms in which the prime is consciously perceived, such as cross-modal priming (Meunier and Longtin, 2007), where only semantically transparent forms (farmer) significantly facilitate the processing of their constituent stem (farm). An alternative account argues that semantic information is accessed early during morphological processing, in parallel with orthographic information (Diependaele et al., 2005; Feldman et al., 2009, 2015). In this account, masked priming effects are argued to show a graded effect depending on the strength of the relationship between stem and whole-form meaning—hence, larger effects for transparent forms and weaker effects for opaque form.

Here we approach the issue of semantic influences on morphological processing from a different perspective, asking about the role of semantic context in early morpho-orthographic segmentation. Can this bottom-up, stimulus-driven process of segmenting potential stems and suffixes be modulated by contextual constraints? The majority of evidence for morpho-orthographic segmentation has come from studies of words in isolation (farmer priming farm), and may therefore to some extent reflect this specific experimental setup. We investigated the effects of context to test how language processing takes place in an environment which is closer to reading in real life, where words are embedded into a wider semantic setting.

Extensive neuroimaging evidence has demonstrated top-down modulation of early processing in domains, such as speech perception (Davis and Johnsrude, 2007) and low-level visual processing (Gazzaley et al., 2005; Rauss et al., 2011). Furthermore, language comprehension and production models have long posited interactivity (McClelland and Rumelhart, 1981), suggesting a key role for contextual information and prior knowledge on bottom-up processes. Given the strong claims concerning blind, data-driven analysis of morpho-orthographic structure, it is therefore important to consider whether this bottom-up process could be constrained by contextual information.

The existing morphological processing literature offers limited evidence. One recent eye-tracking study (Amenta et al., 2015) used a property specific to Italian to examine how sentential context interacts with morpho-orthographic segmentation. In this study, derived Italian words were embedded in sentences that altered word meaning toward either a transparent or opaque interpretation. The authors report stem frequency effects for both transparent and opaque meanings on first fixation duration, a measure of early processing. This suggests that all forms are initially segmented regardless of the context. However, the effect on first fixation duration was facilitatory for transparent meanings and inhibitory for opaque meanings, indicating that semantic information for the stem and suffix is available, and results in an incongruent interpretation for opaque forms.

The effect of sentence context on morphological processing has also been investigated in a cross-modal priming study of German particle verbs (Zwitserlood et al., 2005). These results demonstrated differing priming effects for semantically transparent (e.g., meebrengen, bring along—related to the stem brengen, bring) and semantically opaque verbs (e.g., ombrengen, exterminate—unrelated to the embedded stem brengen) when primed by the meaning of the stem (brengen). Transparent forms showed priming but opaque forms did not, which was interpreted as evidence for separable representations for opaque forms and their constituent stems at the conceptual level. However, it is not clear whether early stages of morphological processing were modulated by the context—before the relationship between the prime and target was consciously processed—which was not directly investigated in this study.

Our goal in this study was to incorporate a semantic context within the masked priming paradigm, to assess if there is an interaction between the context and the analysis of morpho-orthographic structure. In a standard masked priming study, morpho-orthographic segmentation of the prime is indexed by the facilitation of target word recognition (as compared to an unrelated control). When presented in isolation as masked primes, both semantically transparent and opaque forms (farmer, witness) are segmented, resulting in facilitated recognition for the stem targets (Rastle et al., 2004; Marslen-Wilson et al., 2008; McCormick et al., 2008). The critical aspect of our design is the inclusion of a visible prime that preceded the masked prime, which can provide information about the whole-form meaning of the masked prime: e.g., a masked prime witness preceded by a fully visible word jury (see Table 1). We then manipulated how the visible prime was related to the masked prime. A visible prime that is semantically unrelated to the masked prime (e.g., tulip–witness–wit) is not expected to interfere with the morpho-orthographic segmentation of the masked prime. As such, any resultant facilitation of the target would be due to the relationship between the masked prime and target (witness–wit). This context allows us to compare the current results with the existing literature on morpho-orthographic segmentation.

The primary focus of interest, however, was the context where the visible prime was semantically related to the masked prime. For semantically transparent words like farmer, a preceding visible prime like crop is consistent with both the whole-form meaning of the word farmer and its morphological constituents. However, for semantically opaque forms, such as witness preceded by a semantically related word jury, the meaning of the stem wit is incompatible with the semantic context of jury. Based on a form-before-meaning account (Rastle et al., 2004; Crepaldi et al., 2010), all words containing a stem and a suffix are segmented in a bottom-up manner; thus, farmer will prime farm and witness will prime wit. However, given a semantic context that biases the interpretation toward the whole-form meaning (witness → jury/crime/court, etc.), it is unclear whether witness will still be segmented based on a top-down modulation of bottom-up processing.

There are two possible outcomes here: blind morpho-orthographic segmentation could take place regardless of the context—purely based on the bottom-up input—thus both farmer and witness will prime their respective stems even when the semantic context is incongruent with the semantically opaque stem (wit). Alternatively, the context could interact with bottom-up, form-based processing, resulting in a reduced or absent masked priming effect for semantically opaque forms (witness-wit), but still showing priming for semantically transparent forms (farmer-farm). This second prediction is not necessarily inconsistent with a form-before-meaning account, but it would require a re-interpretation of previous results by allowing for contextual modulations on morphological processing when words are not processed in isolation.

In summary, the present study included three conditions and three prime contexts in a modified masked priming design, where an overt semantic prime was followed by a masked prime and a target. The three conditions were: (1) semantically transparent forms (farmer-farm), (2) semantically opaque forms (witness-wit), and (3) stem-only forms (spinach-spin). They were presented in three prime contexts: (1) with an overt prime semantically related to the masked prime (+Semantic +Mask; e.g., jury-witness-wit); (2) with an overt prime semantically unrelated to the masked prime (–Semantic +Mask; e.g., tulip-witness-wit); and (3) a baseline control context, where neither the overt nor the masked prime was related to the target (Control; e.g., tulip-jetty-wit). This final baseline context is not expected to trigger any facilitation of the processing of the target word, thus serving as an overall control.

In the context where the masked prime is preceded by a semantically unrelated prime (Context 2; –Semantic +Mask; e.g., tulip-witness-wit), we expect to see priming in the transparent and opaque conditions but not in the stem-only condition, consistent with the previous literature (e.g., Rastle et al., 2004). The critical context is Context 1, where the masked prime is preceded by a semantically related word (+Semantic +Mask). Here, the primary focus is on the semantically opaque condition (e.g., jury-witness-wit), with the key question being whether opaque forms like witness will still undergo morpho-orthographic segmentation into wit + -ness (and therefore facilitate the recognition of the target wit) when the segmented meaning is inconsistent with the context. If witness no longer primes wit in the context of a semantically related prime jury, this would suggest that external semantic variables can influence early morphological processing.

Finally, the current design included an additional control condition to test for the direct effects of semantic context on the target. This is because the semantic prime is related in meaning to both the masked prime and the target for semantically transparent forms in Context 1 (+Semantic +Mask; e.g., crop-farmer-farm); thus, both primes may play a role in facilitating recognition of the target. To disentangle the contribution of the two primes, this control condition included word triplets in which only the semantic prime was related to the target (+Semantic –Mask; e.g., crow-paler-hawk). If the semantically transparent condition with two related primes (+Semantic +Mask; e.g., crop-farmer-farm) shows faster recognition times compared to the +Semantic –Mask control context, this will further confirm that the masked prime is modulating processing of the target, and that our paradigm is indeed tapping into the intended early stages of visual word recognition.

All errors (5.1% of trials) and all time-outs (defined as responses longer than 1,500 ms; 0.02% of trials) were removed. One item from the stem-only condition (heave) was excluded because of error rates over 50%.

In this study we aimed to test the possible interaction between top-down contextual information and bottom-up morphological analysis. Previous masked priming studies have demonstrated that words are automatically segmented into their constituent parts based on the presence of a stem and a suffix (Longtin and Meunier, 2005; Marslen-Wilson et al., 2008; McCormick et al., 2008; Rastle and Davis, 2008; Beyersmann et al., 2016). However, it is not known whether contextual information can modulate this data-driven segmentation and bias processing toward the whole-form meaning of a complex word.

To test this, we constructed an adapted masked priming design, where an overt semantic prime preceded the masked prime. Semantic priming is a robust effect showing faster and more accurate responses to a target if it is preceded by a semantically related word (Neely, 1991), which can modulate target reading times even at short prime durations (Sereno and Rayner, 1992). Here we focused on using the semantic prime to modulate processing of the masked prime rather than the target. By biasing the interpretation of the masked prime toward the whole-form meaning—the standard role of semantic context in natural language usage—we could assess if early morphological processing could be altered by previous contextual information. The key question was whether the presence of such a context would modulate the amount of morpho-orthographic priming between the masked prime and the target, particularly for semantically opaque pairs like witness-wit—in other words, would witness still prime the stem wit when they are preceded by the semantic context of jury?

To ground our results in the existing literature, we first established that complex words undergo an automatic morpho-orthographic segmentation when presented without an interfering context. To this end we tested priming effects in the context where the masked prime was related to the target but the semantic prime was unrelated to the masked prime (–Semantic +Mask), compared to the baseline (Control). Our results revealed a significant interaction between prime context and condition, showing that both semantically transparent and opaque words (farmer, witness) significantly primed their stems (farm, wit), but that stem-only forms, such as spinach did not prime their stems (spin). Crucially, there was no significant difference between the masked priming effect for transparent and opaque forms. This confirms that the presence of a potential stem and suffix is sufficient for decomposition when there is no informative context for the whole-form meaning, consistent with the existing masked priming literature.

The addition of a semantic context, where the semantic prime is related to the masked prime (+Semantic +Mask; crop-farmer-FARM, jury-witness-WIT), revealed a significant interaction between prime context and condition. Only semantically transparent forms (crop-farmer-FARM) showed significant priming in this context. Semantically opaque forms, on the other hand, did not show a priming effect when presented in the context of a semantically related overt prime (jury-witness-WIT), and the difference between the amount of priming for transparent and the opaque forms was also significant. This absence of priming for opaque forms suggests that morpho-orthographic segmentation can be modulated by the external contextual environment. Stem-only forms (spinach-spin) did not show significant priming in any context, as predicted.

A set of further comparisons directly contrasted morphological priming effects across the three contexts. These data showed that there was no significant difference between the amount of priming for morphologically transparent forms in the context of two primes and a masked prime only (35 and 33 ms, respectively). In contrast, the amount of priming for morphologically opaque forms in the masked prime only context (–Semantic +Mask) was significantly different from that seen in the two prime context (+Semantic +Mask; 20 and 4 ms, respectively), further confirming that external contextual environment modulates morpho-orthographic segmentation for opaque words only.

With the use of this adapted masked priming design, it is important to consider the possible effect of the direct relationship between the overt semantic prime and the target, since both are fully visible. This is especially true in the context where the overt prime is semantically related to the masked prime (+Semantic +Mask), and the masked prime is a transparent form (farmer). In this context, the semantic prime (crop) is also related to the target meaning (farm). This is inherent to semantically transparent words: if the semantic prime is related to the masked prime then it will necessarily be related to the target. Therefore, we cannot rule out that the priming effect seen for the transparent forms in a semantically related context (crop-farmer-FARM) is due to priming from the semantic prime to the target. It is important to note that this only holds for transparent forms in the semantically related context; this is not present in any other condition or context of interest.

To address this issue, we included a control condition in which the semantic prime was related to the target but the masked prime was unrelated (+Semantic –Mask; e.g., hawk-paler-CROW). This allowed us to assess facilitation due to the overt relationship between the semantic prime and target, irrespective of the masked prime. We found significantly faster RTs in the +Semantic +Mask context (crop-farmer-FARM) compared to the control semantic condition (+Semantic –Mask; e.g., hawk-paler-CROW), suggesting that our effects are indeed driven by the processing of the masked prime. Further evidence that the masked prime is playing a key role in this study is demonstrated by the significant priming effect for transparent and opaque forms with an unrelated semantic prime (smooth-farmer-FARM; tulip-witness-WIT). In both of these cases, it is only the masked prime that could facilitate the target.

The finding that contextual information modulates morpho-orthographic segmentation for opaque words like witness, but does not affect priming for transparent words like farmer, appears at first to contradict the form-before-meaning account (Rastle and Davis, 2008). If semantic transparency modulates the amount of masked morphological priming, this could be interpreted as evidence for early morpho-semantic processing, rather than purely morpho-orthographic segmentation. Such interpretation would be more consistent with the form-with-meaning account (Feldman et al., 2009), in which meaning plays an early role in the processing of complex words, and semantic similarity between the masked prime and target determines the size of the priming effect. It is however difficult to position our results fully within either the form-before-meaning or the form-with-meaning account, as they both focus on the role of the word's internal morpho-semantic structure, and neither makes explicit predictions about contextual effects in early morphological analysis.

Whether or not the semantic makeup of an isolated complex word influences its morpho-orthographic segmentation from the very onset, our data unambiguously show that all words with a potential stem and a suffix undergo this automatic analysis—as illustrated by significant and statistically comparable priming for both semantically transparent and semantically opaque words (farmer, witness) in the –Semantic +Mask context, where the masked prime is related to the target (farmer-FARM, witness-WIT). Critically, our results also make clear that external contextual information can modulate this process by biasing the interpretation toward the whole-form meaning (witness as opposed to wit).

One way of accounting for these results is to hypothesize that this reflects rapid integration of semantic information following morpho-orthographic segmentation, similar to the interpretation offered by Amenta et al. (2015). As described earlier, this eye-tracking study embedded derived Italian words into sentences that altered their meanings toward either a transparent or opaque interpretation. Early effects of frequency of the embedded stem were seen for both transparent and opaque meanings, which were facilitatory for transparent meanings and inhibitory for opaque meanings. The authors suggested that all potentially complex forms are automatically decomposed regardless of semantic transparency, but that the meanings of decomposed stems and suffixes are accessed early. This is consistent with evidence from the fast priming paradigm concerning rapid activation of semantics during reading more generally (Sereno and Rayner, 1992). Whilst our results can be accommodated within this hypothesis, they cannot provide a definitive verification, as they leave open another possible interpretation of the locus of the effects.

According to this alternative explanation, the observed reduction of priming for witness-WIT in the context of overtly presented form jury reflects the way these forms are represented at the level of central lexical representations, i.e., in the mental lexicon. A large body of evidence from behavioral and neuroimaging studies suggests that opaque words like witness are represented as “whole forms,” defined as a separate lexical entry with no internal representation of morphemic structure (Bozic et al., 2013a,b). In these cases, the onset-embedded stem like wit constitutes a second, different representation. Data further show that this second representation acts as a strong competitor, delaying the recognition of the derived form in a manner similar to the cohort competition effects (Marslen-Wilson, 1987). Hence, the presentation of an overt semantically related prime jury would facilitate access to the stored whole-word representation of witness. As a result, the whole form witness will become a stronger competitor for the separately represented and semantically unrelated target wit, and morphological priming between them will be weakened or eliminated. Comparable data have been seen in many morphological priming studies, where overtly presented opaque words elicit no priming for their targets (Marslen-Wilson et al., 1994; Rastle et al., 2000).

Due to the very nature of the current (behavioral) data, we cannot pinpoint the exact processing level at which the overt semantic prime like jury modulates the processing of the masked prime witness. Thus, it is difficult to conclude whether the observed results reflect early effects of semantics on morpho-orthographic segmentation of complex words (preventing the incorrect segmentation of witness into wit + -ness), or a consequence of semantic priming between the stored representations of jury and witness at the level of central lexical representations (increasing competition between the whole form and embedded stem target). Regardless of which of the two interpretations better accounts for our data however, we show that top-down semantic context can interfere with early morphological analysis of complex words. This further supports the findings about the key role for contextual information and prior knowledge on bottom-up processes, shown across a variety of cognitive domains (Gazzaley et al., 2005; Davis and Johnsrude, 2007).

An important issue to address in future studies is how morphological segmentation is modulated by different types of contexts. In this study, we primed the whole-form meaning using a semantic prime, but further research could use stronger constraints, such as full sentences with high cloze probability, where we might see further reduction in masked priming for opaque forms. An additional question to pursue is how priming is affected by contexts that prime aspects beyond whole-form meaning—for instance, what would happen if wheat primed corner, where the embedded stem (corn) is now the congruent context? To provide a fuller account of the interaction between bottom-up and top-down processes, magnetoencephalography (MEG) and electroencephalography (EEG) evidence would be integral for tracking both where and when morphological effects emerge in differing contexts.

To conclude, we have provided novel evidence on the role of semantic context in modulating early morphological processing. The presence of a contextual cue to the meaning of the whole form eliminated the priming effect for semantically opaque forms, such that witness no longer primed wit. However, our findings also revealed that blind morpho-orthographic segmentation is triggered in the absence of context—consistent with the form-before-meaning account—with significant masked priming effects for both semantically transparent and opaque forms. The results of this study point to an interaction between top-down information provided by the context and bottom-up analysis during early stages of visual word processing. With the current design, we cannot determine the exact nature of this interaction—whether automatic segmentation is blocked by the semantic context, or whether the top-down semantic information interacts with the resulting stem and suffix following segmentation. Further studies are needed in order to disentangle possible interpretations of findings, but the current results open up an important discussion about the role of contextual information on stimulus-driven processing during early stages of word processing.

This study was carried out in accordance with the recommendations of the Cambridge Psychology Research Ethics Committee with written informed consent from all subjects. All subjects gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the Cambridge Psychology Research Ethics Committee.

CW, RC, and MB designed the study, acquired and analyzed the data, and wrote the manuscript.