BACKGROUND
spoken word comprehension requires a listener to identify a single word among thousands of representations stored in her mental lexicon.
behavioral research suggests that the incoming auditory signal activates multiple lexical representations that match the signal  <cit> , but also representations with partial mismatch to the input  <cit> .
pseudowords like gabinet or mabinet, for example, have been shown to activate the word cabinet.
however, this activation is decreased as compared to a complete match.
thus, the matching of input and stored representations results in a specific activation pattern.
words that completely match the input are strongly activated.
words that partially mismatch the input are less strongly activated.
competition among activated candidate words has been postulated as a mechanism that reduces the number of activated words  <cit> .
strongly activated words inhibit less strongly activated words.
both, graded lexical activation and competition, have been previously investigated using word fragment priming.
a word fragment, which is commonly the onset of a spoken word, is immediately followed by a visual word or a meaningless letter string .
participants are asked to decide whether they saw a word or not.
faster responses for words that match the fragment as compared to unrelated control words have been found.
for example, responses to music are faster when it follows mus than when it follows viba.
this facilitation has been interpreted as reflecting the activation that modality-independent representations of matching words receive from the fragments  <cit>  .
different amounts of overlap between fragment and word modulate reaction times in fragment priming.
for example, responses are faster when a fragment has the same stress as the target word than when fragment and target word differ in stress  <cit> .
a word like music, with stress on the first syllable, is responded to faster when it is preceded by stressed mus than when it is preceded by unstressed mus.
this result illustrates graded lexical activation depending on goodness-of-fit between fragment and word.
furthermore, inhibition has been found when fragments were taken from competitor words.
responses are faster when a word is preceded by an unrelated fragment than when the same word is preceded by a partially mismatching fragment for which a better completion exists  <cit> .
for example, abon taken from the spanish word abonado  inhibits processing of abanico .
event-related brain potentials  recorded for targets in fragment priming reveal a previously undescribed left-hemispheric brain potential  <cit> .
it is called the p <dig> and differentiates matching words from unrelated control words.
difference waves resulting from the subtraction of matching words from unrelated control words reveal more positive amplitudes with a maximum peak at  <dig> ms. comparable p <dig> difference waves have been shown for visual fragments preceding visual words.
therefore, it was concluded that the p <dig> reflects neural processing related to the identification of modality-independent lexical representations.
furthermore, subtle differences in the speech signal such as pitch contour modulate the p <dig> effect.
pitch contour is an important parameter that marks lexical stress.
p <dig> effects reveal that words with a stress pattern that matches the pitch contour of the input are stronger activated than words that do not match in their stress pattern  <cit> .
besides the p <dig> effect, enhanced n <dig> amplitudes are reliably found for unrelated control words in fragment priming.
the n <dig> is a frequently observed erp component in different language related tasks .
it has been argued that the n <dig> amplitude does not reflect automatic lexical activation in priming tasks  <cit> .
it appears more plausible from a vast amount of n <dig> results that the amplitude of this component is inversely related to the effort needed to integrate an incoming word in a preceding context formed by a sentence or a single priming stimulus.
accordingly, the n <dig> might rather be related to post-lexical matching and integration processes than to lexical activation in fragment priming  <cit> .
a lexical account to the n <dig> in word fragment priming is also challenged by the fact that its amplitude is not sensitive to fine-grained activation differences as a function of pitch  <cit> .
therefore, we interpreted the n <dig> as a correlate of strategic effects that are assumed to assist lexical decisions in a priming situation  <cit> .
possible mechanisms that speed up yes-responses to matching words might be a rough phonological matching between prime and target or the expectation of a phonological form, which is established by the fragment.
a phonological account to the n <dig> is supported by n <dig> reduction found for rhyming words  <cit>  or word stem priming  <cit> .
the present study aimed to explore erp correlates of the activation of partially mismatching words following fragments for which better completions exist.
monosyllabic word onset fragments were extracted from german word pairs that had identical first syllables except of the vowel .
three types of fragment-word pairs summarized in table  <dig> were tested: in a match condition, words were preceded by completely matching fragments.
in a mismatch condition, the same words were preceded by fragments extracted from their pair members.
in control conditions, fragments were followed by unrelated control words.
neural correlates of graded lexical activation are shown.
however, neither neurophysiological data nor behavioral results reveal inhibition of partially mismatching words during this early phase of lexical identification.
RESULTS
reaction times and error rates
mean reaction times and error rates are shown in figure 1a.
behavioural measures were subjected to one-way anovas with the three-level factor relatedness .
a main effect of relatedness allowed further step-down analyses of differences between conditions, f =  <dig> , greenhouse-geisser epsilon =  <dig> , corrected p < .
<dig>  responses to completely matching words were faster than responses to unrelated control words, t =  <dig> , p < .
<dig>  similarly, responses to partially mismatching words were faster than responses to unrelated control words, t =  <dig> , p = .
<dig>  nevertheless, subjects' responses were faster for matching than for partially mismatching words, t =  <dig> , p < .
<dig>  the same pattern of results was observed for error rates for which again a main effect of relatedness was observed, f =  <dig> , greenhouse-geisser epsilon =  <dig> , corrected p < .
<dig>  subjects made less errors for matching words than for unrelated control words, t =  <dig> , p < .
<dig>  similarly, subjects made less errors for partially mismatching words than for unrelated control words, t =  <dig> , p < .
<dig>  nevertheless, responses to matching words were more accurate than responses to partially mismatching words, t =  <dig> , p < .
<dig>
in sum, reactions were faster and more accurate for matching words than for partially mismatching words.
this finding goes in line with behavioral results of previous fragment priming experiments  <cit> .
however, the fact that responses for partially mismatching words were not slower than responses for unrelated control words does not replicate previous work.
remember that in a former study subjects responded faster to unrelated control words  than to partially mismatching words .
this has been taken as evidence that better matching completions inhibit partially mismatching words  <cit> .
the present results indicate that inhibition of partially mismatching words is not an obligatory finding in word fragment priming.
taken together present and previous work, it might be concluded that the lengths of the fragments is a factor that modulates inhibition effects.
in contrast to the former study, in which disyllabic fragments were presented as primes  <cit> , monosyllabic fragments were used in the current experiment.
accordingly, the present results suggest that effective competition needs  information exceeding the first syllable of a spoken word and/or  time to exert inhibitory effects.
with respect to : single syllables as used in the present experiment might fully and partly activate a large number of competitors that do not effectively inhibit each other.
in contrast, disyllabic fragments as used in the previous study might fully activate only a few or at least only one word, which effectively inhibits partly activated words.
with respect to : additional processing time provided by disyllabic fragments, which have a longer duration than monosyllabic fragments, might stabilize inhibitory effects.
further research has to explore both possible influences on competition effects.
erps
mean amplitudes for matching words, partially mismatching words and unrelated control words are shown in figure 1b for eight selected electrode sites, respectively.
waveforms were characterized by an n1-p <dig> complex followed by negativity between  <dig> and  <dig> ms, most prominent over frontal electrode positions.
amplitudes of left hemispheric electrodes were sensitive to the experimental manipulation in the time range between  <dig> and  <dig> ms. difference waves showed characteristic p <dig> effects .
analysis of p <dig> effects was identical to a former study with syllabic fragments  <cit> .
starting at approximately  <dig> ms, an n <dig> component was observed over bilateral posterior electrode positions.
the n <dig> effect began earlier and was of shorter duration than that observed in previous fragment priming studies  <cit> .
it was examined using a time window between  <dig> and  <dig> ms.
p350:  <dig> to  <dig> ms
a three-way anova with factors relatedness , hemisphere , and region  was applied to analyze p <dig> effects.
this analysis yielded significant interactions of the factors relatedness, and hemisphere, f =  <dig> , greenhouse-geisser epsilon =  <dig> , corrected p < .001; and relatedness, region and hemisphere, f =  <dig> , greenhouse-geisser epsilon =  <dig> , corrected p = .
<dig>  amplitudes for matching words differed from unrelated control words over both left hemispheric rois, both t ≥  <dig> , both p ≤ .
<dig>  this suggests lexical activation of matching words.
partially mismatching words also showed some degree of lexical activation.
their amplitudes differed from amplitudes of control words over the left anterior roi, t =  <dig> , p = .
<dig>  however, the fact that amplitudes for matching words differed from partially mismatching words over both left hemispheric rois indicates strongest activation for matching words, both t ≥  <dig> , both p ≤ .
<dig>
to sum up, erps elicited over the left hemisphere were sensitive to the experimental manipulation in the time window of the previously reported p <dig> deflection  <cit> .
over left-temporal scalp regions, a positive-going effect with enhanced amplitudes for unrelated control words as compared to matching words replicates former p <dig> results .
in contrast, negative-going erps with enhanced amplitudes for matching words were observed in the time window of the p <dig> over left-anterior regions .
what remains stable across studies is that subtraction of erps for matching or partially mismatching words from erps for unrelated control words results in positive-going difference waves with a maximum at  <dig> ms. therefore, it appears more appropriate to apply the label 'p <dig> effect' to these difference waves than to a positive-going deflection in the erps.
p <dig> effects appear to differ with respect to their scalp topography on an anterior-to-posterior dimension over the left hemisphere.
in the present study p <dig> effects were pronounced over temporo-frontal electrode positions.
in contrast, only temporal electrodes were involved in p <dig> effects found in previous studies  <cit> .
an obvious cause for different p <dig> topographies might be the earlier onset of the n <dig> effect in the present study as compared to the previous studies.
the n <dig> also shows a posterior scalp distribution, but counteracts the p <dig> effect in polarity of the elicited differences.
the earlier beginning of the n <dig> effect in the present study may have canceled out the posterior part of the p <dig> effect resulting in the observed temporo-frontal scalp topography.
the present results are consistent with the idea that p <dig> effects are closely correlated to the activation status of lexical entries in a modality-independent mental lexicon.
matching words, which are strongly activated by the input, elicit large p <dig> difference waves.
partially mismatching words, which are less strongly activated by the input, elicit reduced p <dig> difference waves.
however, from the present and the previous results it is difficult to distinguish whether the p <dig> effect reflects a surplus in positivity for unrelated control words or a surplus in negativity for matching words.
as already discussed p <dig> effects were related to different erp deflections across the present study and previous studies.
it has been suggested that reduced positive-going amplitudes for matching words are a correlate of facilitated lexical identification resulting from pre-activation of lexical entries  <cit> .
in contrast, enhanced negative erp amplitudes for matching words over left temporo-frontal electrodes, which were observed in the present study, might suggest that p <dig> effects directly result from the activation status of lexical entries.
negative-going left temporo-frontal erps in the time window of the p <dig> effect look very similar to an n <dig> effect reported earlier  <cit> .
the n <dig>  which also shows a temporo-frontal scalp distribution, was found to be enhanced for words primed by semantic associates as compared to unprimed words.
this contrasts the n <dig> priming effect classically showing reduced amplitudes for words with semantic relation to their preceding primes .
both the n <dig> effect in semantic priming and the p <dig> effect in word fragment priming can be functionally separated from the n <dig> effect.
interestingly enough, the n <dig> was interpreted as a correlate of semantic or lexical activation.
this is in line with the present interpretation of the p <dig> difference wave being related to lexical activation.
it remains to be investigated whether the neural activation mechanism that is reflected in the p <dig> difference wave might also underlie the previously reported n <dig>
minimum norm calculations were conducted to elucidate the localization of neural processes underlying p <dig> difference waves.
results suggest a left centro-temporal origin of neural sources engaged in the processing of both matching and partially mismatching words .
crucially, minimum norm solutions in both conditions differ only in strength of dipole activation but not in estimated neural sources.
these results clearly point to a unique underlying left-temporal source for processes that are involved in the mapping of speech input onto modality-independent lexical representations.
the underlying neuronal network was stronger activated by matching than by partially mismatching words.
the minimum norm solutions suggest a relation between the p <dig> effect in the erp and an m <dig> effect found in magnetic brain responses  <cit> .
the m <dig> has been characterized as an automatic early component, which appears to be related to lexical access in visual word processing  <cit> .
time ranges of p <dig> difference waves and m <dig> are comparable  <cit> .
furthermore, source analyses for both neurophysiological correlates point to left-temporal neural activation.
both, the p <dig> and the m <dig>  might index automatic spreading activation across lexical entries.
they provide new means to explore aspects of early word processing and the underlying neuronal mechanisms.
n400:  <dig> to  <dig> ms
n <dig> effects were analyzed using the same statistical design as for p <dig> effects .
the three-way anova yielded significant interactions of the factors relatedness and region, f =  <dig> , greenhouse geisser epsilon =  <dig> , corrected p < .
<dig>  relatedness and hemisphere, f =  <dig> , greenhouse geisser epsilon =  <dig> , corrected p < .
<dig>  and relatedness, region, and hemisphere f =  <dig> , greenhouse geisser epsilon =  <dig> , corrected p < .
<dig>  for both posterior rois matching words elicited reduced amplitudes of the n <dig> as compared to unrelated control words, both t =  <dig> , both p = .
<dig>  similarly, partially mismatching words elicited reduced amplitudes of the n <dig> over both posterior rois, both t ≥  <dig> , both p ≤ .
<dig>  however, n <dig> amplitudes for matching and partially mismatching words did not differ significantly, t ≤  <dig> , n.s.
thus, in contrast to p <dig> difference waves and reaction times, n <dig> amplitude did not differentiate matching words and partially mismatching words.
the present n <dig> results go in parallel with the earlier finding that the n <dig> is not sensitive to a mismatch between the pitch of a fragment and the stress pattern of a succeeding word  <cit> .
taken together, results of both studies indicate an insensitivity of the n <dig> to subtle differences between fragment and word.
they support an interpretation of the n <dig> as a correlate of neural processes that operate at a post-lexical level, and indicate that behavioral responses in fragment priming are modulated by more than lexical activation.
phonological matching has been postulated as a possible mechanism that is reflected in the n <dig> in fragment priming  <cit> .
note that both, matching words and partially mismatching words, are phonologically related to the fragments , whereas unrelated control words show no phonological relation to their primes .
the fact that both, matching words and partially mismatching words, elicit reduced n <dig> amplitudes confirms the assumption that processes underling the n <dig> provide a superficial matching or expectation that speeds up yes-responses to words with some phonological relation to the fragment.
a phonological account to the n <dig> is also suggested by n <dig> reduction for rhyming words  <cit>  or for word stem priming  <cit> .
CONCLUSIONS
the present results indicate that fragmentary word information modulates different aspects of neural target processing.
this is reflected by two separate erp correlates, namely p <dig> and n <dig> effects.
both can be distinguished as separate neurophysiological deflections in accordance to several relevant characteristics .
they differ with respect to latency, scalp topography, polarity of the elicited differences, and sensitivity to the experimental manipulation.
therefore, p <dig> and n <dig> effects probably reflect at least two different neuronal processes, which both precede and modulate behavioral responses in fragment priming.
p <dig> effects on the one hand appear to be related to the fine grained mapping of the acoustic input onto lexical representations.
n <dig> effects on the other hand might be related to phonological matching between fragment and word.
this argumentation leads to the conclusion that behavioral data, which are preceded by p <dig> and n <dig> effects, reflect outcomes of both processes.
erps, in particular p <dig> effects, allow investigating lexical activation more directly than behavioral data.
both, reaction times and p <dig> difference waves, suggest that partially mismatching lexical representations, which diverge from spoken word fragments only in the vowel of the first syllable, receive slight activation from the speech input.
in contrast to earlier findings  <cit> , both measures reveal that partially mismatching representations are not inhibited by better matching completions.
thus, the present data do not support a strong notion of competition between activated lexical candidates at early stages of lexical processing.
they reveal that the human speech recognition system does not strictly inhibit alternative candidates from early lexical activation.
factors that modulate competition effects, such as the length of the fragments, have to be focus of future research.
finally, the neuronal sources underlying the activation of modality-independent lexical representations can be studied with fragment priming in more detail.
erps in word fragment priming indicate that activation of representations that receive input from both, spoken and written words, appears to be a left-hemispheric function with underlying neuronal sources in the centro-temporal cortex.
although these neuronal sources appear to be separate from written word from representations in the left fusiform gyrus  <cit> , a relation to speech representations in the left superior temporal sulcus  <cit>  can be assumed.
in light of the primacy of auditory language comprehension in ontogenetic development, the question emerges whether modality-independent lexical representations are identical to speech representations.
the p <dig> effect seems to be a powerful neurophysiological means to address this and related questions regarding neuronal bases of lexical access in human language comprehension.

 spoken word comprehension requires a listener to identify a single word among thousands of representations stored in her mental lexicon. behavioral research suggests that the incoming auditory signal activates multiple lexical representations that match the signal, but also representations with partial mismatch to the input. pseudowords like gabinet or mabinet, for example, have been shown to activate the word cabinet. however, this activation is decreased as compared to a complete match. thus, the matching of input and stored representations results in a specific activation pattern. words that completely match the input are strongly activated. words that partially mismatch the input are less strongly activated. competition among activated candidate words has been postulated as a mechanism that reduces the number of activated words. strongly activated words inhibit less strongly activated words. both, graded lexical activation and competition, have been previously investigated using word fragment priming. a word fragment, which is commonly the onset of a spoken word, is immediately followed by a visual word or a meaningless letter string. participants are asked to decide whether they saw a word or not. faster responses for words that match the fragment as compared to unrelated control words have been found. for example, responses to music are faster when it follows mus than when it follows viba. this facilitation has been interpreted as reflecting the activation that modality-independent representations of matching words receive from the fragments. different amounts of overlap between fragment and word modulate reaction times in fragment priming. for example, responses are faster when a fragment has the same stress as the target word than when fragment and target word differ in stress. a word like music, with stress on the first syllable, is responded to faster when it is preceded by stressed mus than when it is preceded by unstressed mus. this result illustrates graded lexical activation depending on goodness-of-fit between fragment and word. furthermore, inhibition has been found when fragments were taken from competitor words. responses are faster when a word is preceded by an unrelated fragment than when the same word is preceded by a partially mismatching fragment for which a better completion exists. for example, abon taken from the spanish word abonado inhibits processing of abanico. event-related brain potentials recorded for targets in fragment priming reveal a previously undescribed left-hemispheric brain potential. it is called the p and differentiates matching words from unrelated control words. difference waves resulting from the subtraction of matching words from unrelated control words reveal more positive amplitudes with a maximum peak at ms. comparable p difference waves have been shown for visual fragments preceding visual words. therefore, it was concluded that the p reflects neural processing related to the identification of modality-independent lexical representations. furthermore, subtle differences in the speech signal such as pitch contour modulate the p effect. pitch contour is an important parameter that marks lexical stress. p effects reveal that words with a stress pattern that matches the pitch contour of the input are stronger activated than words that do not match in their stress pattern. besides the p effect, enhanced n amplitudes are reliably found for unrelated control words in fragment priming. the n is a frequently observed erp component in different language related tasks. it has been argued that the n amplitude does not reflect automatic lexical activation in priming tasks. it appears more plausible from a vast amount of n results that the amplitude of this component is inversely related to the effort needed to integrate an incoming word in a preceding context formed by a sentence or a single priming stimulus. accordingly, the n might rather be related to post-lexical matching and integration processes than to lexical activation in fragment priming. a lexical account to the n in word fragment priming is also challenged by the fact that its amplitude is not sensitive to fine-grained activation differences as a function of pitch. therefore, we interpreted the n as a correlate of strategic effects that are assumed to assist lexical decisions in a priming situation. possible mechanisms that speed up yes-responses to matching words might be a rough phonological matching between prime and target or the expectation of a phonological form, which is established by the fragment. a phonological account to the n is supported by n reduction found for rhyming words or word stem priming. the present study aimed to explore erp correlates of the activation of partially mismatching words following fragments for which better completions exist. monosyllabic word onset fragments were extracted from german word pairs that had identical first syllables except of the vowel. three types of fragment-word pairs summarized in table were tested: in a match condition, words were preceded by completely matching fragments. in a mismatch condition, the same words were preceded by fragments extracted from their pair members. in control conditions, fragments were followed by unrelated control words. neural correlates of graded lexical activation are shown. however, neither neurophysiological data nor behavioral results reveal inhibition of partially mismatching words during this early phase of lexical identification.  reaction times and error rates mean reaction times and error rates are shown in figure 1a. behavioural measures were subjected to one-way anovas with the three-level factor relatedness. a main effect of relatedness allowed further step-down analyses of differences between conditions, f =, greenhouse-geisser epsilon =, corrected p <. responses to completely matching words were faster than responses to unrelated control words, t =, p <. similarly, responses to partially mismatching words were faster than responses to unrelated control words, t =, p =. nevertheless, subjects' responses were faster for matching than for partially mismatching words, t =, p <. the same pattern of results was observed for error rates for which again a main effect of relatedness was observed, f =, greenhouse-geisser epsilon =, corrected p <. subjects made less errors for matching words than for unrelated control words, t =, p <. similarly, subjects made less errors for partially mismatching words than for unrelated control words, t =, p <. nevertheless, responses to matching words were more accurate than responses to partially mismatching words, t =, p <. in sum, reactions were faster and more accurate for matching words than for partially mismatching words. this finding goes in line with behavioral results of previous fragment priming experiments. however, the fact that responses for partially mismatching words were not slower than responses for unrelated control words does not replicate previous work. remember that in a former study subjects responded faster to unrelated control words than to partially mismatching words. this has been taken as evidence that better matching completions inhibit partially mismatching words. the present results indicate that inhibition of partially mismatching words is not an obligatory finding in word fragment priming. taken together present and previous work, it might be concluded that the lengths of the fragments is a factor that modulates inhibition effects. in contrast to the former study, in which disyllabic fragments were presented as primes, monosyllabic fragments were used in the current experiment. accordingly, the present results suggest that effective competition needs information exceeding the first syllable of a spoken word and/or time to exert inhibitory effects. with respect to: single syllables as used in the present experiment might fully and partly activate a large number of competitors that do not effectively inhibit each other. in contrast, disyllabic fragments as used in the previous study might fully activate only a few or at least only one word, which effectively inhibits partly activated words. with respect to: additional processing time provided by disyllabic fragments, which have a longer duration than monosyllabic fragments, might stabilize inhibitory effects. further research has to explore both possible influences on competition effects. erps mean amplitudes for matching words, partially mismatching words and unrelated control words are shown in figure 1b for eight selected electrode sites, respectively. waveforms were characterized by an n1-p complex followed by negativity between and ms, most prominent over frontal electrode positions. amplitudes of left hemispheric electrodes were sensitive to the experimental manipulation in the time range between and ms. difference waves showed characteristic p effects. analysis of p effects was identical to a former study with syllabic fragments. starting at approximately ms, an n component was observed over bilateral posterior electrode positions. the n effect began earlier and was of shorter duration than that observed in previous fragment priming studies. it was examined using a time window between and ms. p350: to ms a three-way anova with factors relatedness, hemisphere, and region was applied to analyze p effects. this analysis yielded significant interactions of the factors relatedness, and hemisphere, f =, greenhouse-geisser epsilon =, corrected p <.001; and relatedness, region and hemisphere, f =, greenhouse-geisser epsilon =, corrected p =. amplitudes for matching words differed from unrelated control words over both left hemispheric rois, both t ≥, both p ≤. this suggests lexical activation of matching words. partially mismatching words also showed some degree of lexical activation. their amplitudes differed from amplitudes of control words over the left anterior roi, t =, p =. however, the fact that amplitudes for matching words differed from partially mismatching words over both left hemispheric rois indicates strongest activation for matching words, both t ≥, both p ≤. to sum up, erps elicited over the left hemisphere were sensitive to the experimental manipulation in the time window of the previously reported p deflection. over left-temporal scalp regions, a positive-going effect with enhanced amplitudes for unrelated control words as compared to matching words replicates former p results. in contrast, negative-going erps with enhanced amplitudes for matching words were observed in the time window of the p over left-anterior regions. what remains stable across studies is that subtraction of erps for matching or partially mismatching words from erps for unrelated control words results in positive-going difference waves with a maximum at ms. therefore, it appears more appropriate to apply the label'p effect' to these difference waves than to a positive-going deflection in the erps. p effects appear to differ with respect to their scalp topography on an anterior-to-posterior dimension over the left hemisphere. in the present study p effects were pronounced over temporo-frontal electrode positions. in contrast, only temporal electrodes were involved in p effects found in previous studies. an obvious cause for different p topographies might be the earlier onset of the n effect in the present study as compared to the previous studies. the n also shows a posterior scalp distribution, but counteracts the p effect in polarity of the elicited differences. the earlier beginning of the n effect in the present study may have canceled out the posterior part of the p effect resulting in the observed temporo-frontal scalp topography. the present results are consistent with the idea that p effects are closely correlated to the activation status of lexical entries in a modality-independent mental lexicon. matching words, which are strongly activated by the input, elicit large p difference waves. partially mismatching words, which are less strongly activated by the input, elicit reduced p difference waves. however, from the present and the previous results it is difficult to distinguish whether the p effect reflects a surplus in positivity for unrelated control words or a surplus in negativity for matching words. as already discussed p effects were related to different erp deflections across the present study and previous studies. it has been suggested that reduced positive-going amplitudes for matching words are a correlate of facilitated lexical identification resulting from pre-activation of lexical entries. in contrast, enhanced negative erp amplitudes for matching words over left temporo-frontal electrodes, which were observed in the present study, might suggest that p effects directly result from the activation status of lexical entries. negative-going left temporo-frontal erps in the time window of the p effect look very similar to an n effect reported earlier. the n which also shows a temporo-frontal scalp distribution, was found to be enhanced for words primed by semantic associates as compared to unprimed words. this contrasts the n priming effect classically showing reduced amplitudes for words with semantic relation to their preceding primes. both the n effect in semantic priming and the p effect in word fragment priming can be functionally separated from the n effect. interestingly enough, the n was interpreted as a correlate of semantic or lexical activation. this is in line with the present interpretation of the p difference wave being related to lexical activation. it remains to be investigated whether the neural activation mechanism that is reflected in the p difference wave might also underlie the previously reported n minimum norm calculations were conducted to elucidate the localization of neural processes underlying p difference waves. results suggest a left centro-temporal origin of neural sources engaged in the processing of both matching and partially mismatching words. crucially, minimum norm solutions in both conditions differ only in strength of dipole activation but not in estimated neural sources. these results clearly point to a unique underlying left-temporal source for processes that are involved in the mapping of speech input onto modality-independent lexical representations. the underlying neuronal network was stronger activated by matching than by partially mismatching words. the minimum norm solutions suggest a relation between the p effect in the erp and an m effect found in magnetic brain responses. the m has been characterized as an automatic early component, which appears to be related to lexical access in visual word processing. time ranges of p difference waves and m are comparable. furthermore, source analyses for both neurophysiological correlates point to left-temporal neural activation. both, the p and the m might index automatic spreading activation across lexical entries. they provide new means to explore aspects of early word processing and the underlying neuronal mechanisms. n400: to ms n effects were analyzed using the same statistical design as for p effects. the three-way anova yielded significant interactions of the factors relatedness and region, f =, greenhouse geisser epsilon =, corrected p <. relatedness and hemisphere, f =, greenhouse geisser epsilon =, corrected p <. and relatedness, region, and hemisphere f =, greenhouse geisser epsilon =, corrected p <. for both posterior rois matching words elicited reduced amplitudes of the n as compared to unrelated control words, both t =, both p =. similarly, partially mismatching words elicited reduced amplitudes of the n over both posterior rois, both t ≥, both p ≤. however, n amplitudes for matching and partially mismatching words did not differ significantly, t ≤, n.s. thus, in contrast to p difference waves and reaction times, n amplitude did not differentiate matching words and partially mismatching words. the present n results go in parallel with the earlier finding that the n is not sensitive to a mismatch between the pitch of a fragment and the stress pattern of a succeeding word. taken together, results of both studies indicate an insensitivity of the n to subtle differences between fragment and word. they support an interpretation of the n as a correlate of neural processes that operate at a post-lexical level, and indicate that behavioral responses in fragment priming are modulated by more than lexical activation. phonological matching has been postulated as a possible mechanism that is reflected in the n in fragment priming. note that both, matching words and partially mismatching words, are phonologically related to the fragments, whereas unrelated control words show no phonological relation to their primes. the fact that both, matching words and partially mismatching words, elicit reduced n amplitudes confirms the assumption that processes underling the n provide a superficial matching or expectation that speeds up yes-responses to words with some phonological relation to the fragment. a phonological account to the n is also suggested by n reduction for rhyming words or for word stem priming.  the present results indicate that fragmentary word information modulates different aspects of neural target processing. this is reflected by two separate erp correlates, namely p and n effects. both can be distinguished as separate neurophysiological deflections in accordance to several relevant characteristics. they differ with respect to latency, scalp topography, polarity of the elicited differences, and sensitivity to the experimental manipulation. therefore, p and n effects probably reflect at least two different neuronal processes, which both precede and modulate behavioral responses in fragment priming. p effects on the one hand appear to be related to the fine grained mapping of the acoustic input onto lexical representations. n effects on the other hand might be related to phonological matching between fragment and word. this argumentation leads to the conclusion that behavioral data, which are preceded by p and n effects, reflect outcomes of both processes. erps, in particular p effects, allow investigating lexical activation more directly than behavioral data. both, reaction times and p difference waves, suggest that partially mismatching lexical representations, which diverge from spoken word fragments only in the vowel of the first syllable, receive slight activation from the speech input. in contrast to earlier findings, both measures reveal that partially mismatching representations are not inhibited by better matching completions. thus, the present data do not support a strong notion of competition between activated lexical candidates at early stages of lexical processing. they reveal that the human speech recognition system does not strictly inhibit alternative candidates from early lexical activation. factors that modulate competition effects, such as the length of the fragments, have to be focus of future research. finally, the neuronal sources underlying the activation of modality-independent lexical representations can be studied with fragment priming in more detail. erps in word fragment priming indicate that activation of representations that receive input from both, spoken and written words, appears to be a left-hemispheric function with underlying neuronal sources in the centro-temporal cortex. although these neuronal sources appear to be separate from written word from representations in the left fusiform gyrus, a relation to speech representations in the left superior temporal sulcus can be assumed. in light of the primacy of auditory language comprehension in ontogenetic development, the question emerges whether modality-independent lexical representations are identical to speech representations. the p effect seems to be a powerful neurophysiological means to address this and related questions regarding neuronal bases of lexical access in human language comprehension. 
minimum norm solutions point to a left hemispheric centro-temporal source of the p effect in both conditions. erps for matching and unrelated control words differed between and ms. difference waves replicate a left-hemispheric p effect in this time window. event-related brain potentials were recorded for written words following spoken word onsets that either matched, partially mismatched, or were unrelated. results suggest that neural processing of matching words does not inhibit processing of partially mismatching words during early stages of lexical identification. furthermore, the present results indicate that neurophysiological correlates observed in fragment priming reflect different aspects of target processing that are cumulated in behavioural responses. particularly the left-hemispheric p difference potential appears to be closely related to fine-grained activation differences of modality-independent representations in the listeners' mental lexicon. previous psycholinguistic research postulated the activation of multiple words in the listeners' mental lexicon which compete for recognition. the p is interpreted as a neurophysiological index for the activation of matching words in the listeners' mental lexicon. in the present study neurophysiological correlates related to mismatching information in lexical access were investigated with a fragment priming paradigm. a left-hemispheric neuronal network engaged in lexical access appears to be gradually activated by matching and partially mismatching words. this neurophysiological index might guide future studies aimed at investigating neural aspects of lexical access. in contrast to the p and the behavioural responses, a brain potential ranging between and ms was found to be equally reduced for matching and partially mismatching words as compared to unrelated control words.
 in the present study neurophysiological correlates related to mismatching information in lexical access were investigated with a fragment priming paradigm. event-related brain potentials were recorded for written words following spoken word onsets that either matched, partially mismatched, or were unrelated. previous psycholinguistic research postulated the activation of multiple words in the listeners' mental lexicon which compete for recognition. accordingly, matching words were assumed to be strongly activated competitors, which inhibit less strongly activated partially mismatching words.  erps for matching and unrelated control words differed between and ms. difference waves replicate a left-hemispheric p effect in this time window. although smaller than for matching words, a p effect and behavioural facilitation was also found for partially mismatching words. minimum norm solutions point to a left hemispheric centro-temporal source of the p effect in both conditions. the p is interpreted as a neurophysiological index for the activation of matching words in the listeners' mental lexicon. in contrast to the p and the behavioural responses, a brain potential ranging between and ms was found to be equally reduced for matching and partially mismatching words as compared to unrelated control words. this latter effect might be related to strategic mechanisms in the priming situation.  a left-hemispheric neuronal network engaged in lexical access appears to be gradually activated by matching and partially mismatching words. results suggest that neural processing of matching words does not inhibit processing of partially mismatching words during early stages of lexical identification. furthermore, the present results indicate that neurophysiological correlates observed in fragment priming reflect different aspects of target processing that are cumulated in behavioural responses. particularly the left-hemispheric p difference potential appears to be closely related to fine-grained activation differences of modality-independent representations in the listeners' mental lexicon. this neurophysiological index might guide future studies aimed at investigating neural aspects of lexical access. 