2.3 Discussion
Our results did not show any evidence of early ERP components linked to
the processing of spoken emotionally laden words. Notably, we did not
find that negatively or positively valenced words evoked an EPN compared
to neutral words. This result is in line with several previous studies,
which only showed effects starting at 370 ms (Grass et al. 2016; Kanske
& Kotz, 2011; Rohr & Rahman, 2015) or substantially later, only after
word offset (Hatzidaki et al., 2015). In contrast, Mittermeier and
colleagues (2011) reported increased early negativity, on the P2
component, for auditory words with both negative and positive
connotations, but only in comparison to neutral tones (and only reported
for Pz). The very early effects reported by Mettermeier (2011),
replicated by Jaspers-Fayer and colleagues (2012), may nonetheless be
linked to their design, which included only ten auditory words that were
repeated numerous times. This may have allowed participants to
anticipate the words and access meaning from their onset. In addition,
as no neutral words were included, it is difficult to ascertain whether
the reported effect was due to the valence of the linguistic stimuli or
to differences in task demands, i.e. the ease of discriminating between
two tones vs. identifying linguistic content. In line with this,
previous results have shown that the N1-P2 complex is modulated by the
physical characteristics of auditory stimuli but not by their linguistic
(emotional) content (Grass et al., 2016). The lack of early effects in
present study may be linked to the characteristics of our auditory
stimuli in particular and to auditory processing of words in general,
which is incremental in nature. The Mandarin words we presented were
disyllabic and full lexical access was not possible until participants
heard the second syllable, which on average occurred at roughly 400
msec. No stimulus was repeated such that participants could not
anticipate words. Our results differ from Grass’s study (2016), which
reported an enhanced frontal positivity and parieto-occipital negativity
for valenced words between 370-540 msec post-stimulus, likely due to the
differences in task requirement: While our study used a valence
judgement task, Grass’s study employed a one-back task that encouraged
participants to recall previous stimuli, leading to increased priming
effect through contextual association. Valenced words have been shown to
exhibit stronger inter-item associations and higher semantic relatedness
(Buchanan et al., 2006), suggesting that valenced words may prime each
other more effectively. This superior priming among valenced words could
result in facilitated processing for valenced words during the one-back
task. Instead, our findings align more closely with Hatzidaki’s (2015)
study, which also used a valence judgement task and reported a late LPC
between 600-950 msec post-stimulus. Although the mean amplitudes of ERPs
for our Negative or Positive words were numerically larger than for
Neutral words in later time windows (500-800 msec and 800-1100 msec),
this pattern did not reach statistical significance.
In relation to the behavioral classification of the auditory words, our
results showed that participants’ valence ratings of Mandarin words
generally corresponded to the English norms, with some discrepancies.
Previous studies of emotion lexicons have shown cultural differences of
emotion concept, including appraisal. That is, while an emotion word may
have equivalent translations in two languages, speakers of those
languages may still have different evaluations of associated events or
consequences with positive or negative connotation (for a review, see
Pavlenko, 2008). Noting that our experimental words were translated from
English to Mandarin and categorized into one of three given valence
types based on an affective database of English words, our behavioral
data is thus consistent with this account, reflecting that Mandarin
speakers and English speakers did not always appraise lexical items that
carry emotional connotations identically.
EXPERIMENT 2
As outlined in the general introduction, people tend to show enhanced
recall and recognition of emotional stimuli compared to neutral ones
(for a review, see Tyng et al., 2017). Such “emotion-memory” effects
are less widely documented for auditory than visually presented stimuli.
We capitalized on our participants having taken part in the first,
auditory experiment to further examine this question. In the following
experiment, stimuli were presented in written format and participants
were required to identify those words that they had heard in the
immediately prior experiment among an equal number of foils with
positive, negative or neutral valence ratings. Participants were not
informed of the second experiment prior to the completion of the
first. The second experiment thus provided us with a means to examine
the impact of valence and arousal on memory encoding as well as allowing
a direct comparison of the electrophysiological response to emotionally
laden words across auditory and written format. To our knowledge, while
numerous studies have examined the ERP response to emotion words in
either written or auditory format, only one study (Rohr & Rahman, 2015)
to date has directly compared the two for the same set of words.
Distinct patterns were reported as a function of presentation, with an
enhanced negativity, specifically for negative compared to neutral words
for printed words, while no reliable valence effect, but an unexpected
negativity over central ROI for negative words compared to neutral words
in auditory presentation.