DR. B. M. ABROL AWARD FOR BEST PAPER IN SPEECH - 2011
LEXICAL INHIBITORY MECHANISM IN PERSONS WITH
STUTTERING: A PRELIMINARY STUDY
Author
Thejaswi.D
III Year BASLP
Nitte Institute of Speech and Hearing, Mangalore.
ISHA Student membership no: SM-1346
Email: thejaswi07@gmail.com
Guide
Manjunath.N
Lecturer
Department of Speech-language pathology
Nitte Institute of Speech and Hearing, Mangalore.
ISHA membership no: L-1357
Email: man_n94@yahoo.com
LEXICAL INHIBITORY MECHANISM IN PERSONS WITH STUTTERING: A
PRELIMINARY STUDY
ABSTRACT
INTRODUCTION:
Stuttering is an enigmatic disorder in the field of speech pathology. Many
theories have been put forth to explain the nature and cause of stuttering. In recent
years large attention has been paid to explain the processes involved in language
and motor execution in persons with stuttering. Different models have been
proposed to explain the processes in the language production and lexical access in
this population. Lexical access refers to the processes by which speakers retrieve
and encode words for expression. Lexical retrieval models illustrate both activation
and inhibition between concepts, words and phonemes.
The present study adopts priming paradigm to study the lexical access in
persons with stuttering. Meyes & Schvanevelt (1971) found that in normal speakers,
the speech onset latencies were shortest in homogeneous condition than the
heterogeneous condition. Packman, Onslow, Coombes & Goodwin (2001)
investigated the first two stages of lexical access of Levelt’s model in persons with
stuttering through non-word reading. They concluded that stutterers did not exhibit
any problem while non-word reading and hence devoid of any problem at these
levels. The underlying rationale behind priming is that when the priming word is
semantically related to the target word, it facilitates the recognition of target word and
semantically unrelated priming word leads to inhibition of the target stimuli (Perkins,
Kent & Curlee, 1993). When semantic activation spreads from one concept to its
related concepts, inhibition is recruited so that competition between related concepts
can be overcome and a target production is achieved. Lexical inhibitory processing is
typically measured using a negative priming (NP) task (Fox, 1995; Houghton and
Tipper, 1994), it refers to delayed response identification time to a target stimulus
that has been previously ignored. It has been known from literature that different
populations have different levels of inhibitory control and this can be revealed by
using NP task. Hence in this study the negative priming paradigm has been used to
know the lexical inhibitory mechanism in persons with stuttering.
NEED FOR THE PRESENT STUDY:
As per literature, different populations have different levels of inhibitory control
and this can be revealed by using NP task. In this study, the negative priming
paradigm has been used to know the lexical inhibitory mechanism in persons with
stuttering. Hence, the purpose of the study was to note the lexical inhibitory
mechanism through NP task in persons with stuttering and normal individuals.
METHOD:
Subjects:
A total of 40 male subjects participated in the study. Group I consisted of 20
persons with stuttering in the age range of 18 to 33 years (mean 23.5 years). Group II
consisted of 20 age matched normal individuals (mean 22.1 years). All the subjects
were native speakers of Kannada language.
Test stimuli and apparatus:
Five categories of nouns with each five set of five line drawing pictures
(5*5=25) were selected. The five categories were vehicles, fruits, musical
instruments, clothing, and animal selected from the norms developed in Kannada
(Wasim, 2008). For this study, prime and probe trial pictures were developed
comprising of two super imposed pictures in each trial and presented in ordered
sequence. The target was outlined with red colored ink and distractor was outlined
with blue colored ink. The stimuli were programmed with DmDx software which
controlled the presentation of the prime and the probe.
Procedure:
Each subject was tested individually in a quiet room and each session lasted for
about 30 minutes. The subjects were seated at a comfortable viewing distance from the
monitor with the microphone approximately one inch in front of their lips. The stimuli
were presented in two conditions to note the negative priming effect in persons with
stuttering and normal subjects. Condition 1 is the semantically ignored condition in
which ignored picture in the prime trial and target picture in the probe trial are
categorically related. Condition 2 is the control condition where unrelated picture in
prime and probe trial were presented. The subjects were instructed to name the
target picture outlined with red colour for both the conditions as soon as possible.
Thus, the difference in reaction times between the conditions represents the NP
effect. During each block of the experiment, the researcher sat behind the subjects
and recorded by hand any technical problems and any errors made. The
presentation of the blocks and stimuli across each condition was randomized across
subjects. A total of 50 responses were collected from each subject and analyzed
further.
Statistical analysis:
The data collected from the subjects were tabulated. SPSS (Version 10) was
used for statistical analysis. Independent and paired t-test was used to note any
statistically significant difference between the groups and conditions within the group
respectively.
RESULTS AND DISCUSSION:
The results were analyzed for two negative priming conditions. For condition I
and condition II, normal individuals had mean reaction time of 889 msec and 849
msec; for persons with stuttering it was 1149 msec and 1131 msec respectively. There
was statistically significant difference in mean reaction time for condition I and condition
II between group I and group II subjects (p<0.05). On treating the data with paired t-test
within the group for condition I and condition II, significant negative priming effect was
noted in group I (p>0.05) and absent in group II (p<0.05).
The overall longer reaction time for condition I and condition II in persons with
stuttering may be due to the abnormality at the level of the nodes, which represent the
semantic pathways and it makes them slower to retrieve the lexical information from
the mental lexicon that may contribute to the stuttering block. Also, the present study
provides evidence for the role of inhibitory processing resources in selective attention
and for their applicability to lexical retrieval in stutterers. The NP effect can be
explained with the process of ‘spreading inhibition’ in semantic memory networks,
analogous to that of ‘spreading activation’ (Meyer & Schvaneveldt, 1975; Collins &
Loftus, 1975). Thus, if a stimulus has been ignored during selection of a simultaneous
target, the internal representation is associated with inhibition, which may spread to
related concepts, causing a slower reaction time during NP which was seen in normal
subjects. This reduction in reaction time may be because of the intact spreading
inhibition system. Hence, the reason behind the absence of NP in persons with
stuttering may be attributed to the deficit of spreading inhibition system.
CONCLUSION:
The aim of the present study was to investigate lexical inhibitory processing in
stutterers using NP task. The data was analyzed for accurate responses and
reaction time measurements. Results revealed significant differences for condition I
and condition II between normal subjects and persons with stuttering. The absence
of NP effect in stutterers may be attributed to reduced ‘spreading inhibition’ process.
The therapy techniques implemented with stutterers should focus on NP to improve
the lexical inhibitory process and reduce cognitive stress during moments of
stuttering instances and thus effectively manage the persons with stuttering. Further
studies need to be conducted with increased sophistication of measurement and on
a larger sample size to validate the results. Moreover, negative priming may be
used to determine any insufficiency of the inhibition process, enabling treatment to
be devised that addresses this insufficiency in affected individuals.