Table of Contents    
Year : 2021  |  Volume : 12  |  Issue : 1  |  Page : 75-83  

Measuring Effects of Competing Swallowing-Cognitive Task on 100-ml Water Swallowing and Number Recognition: A Crossover Comparative Study in Healthy Young and Middle-Aged Adults

Department of Audiology and Speech Language Pathology, Nitte Institute of Speech and Hearing, Mangalore, Karnataka, India

Date of Submission16-Mar-2020
Date of Decision14-Apr-2020
Date of Acceptance25-May-2020
Date of Web Publication27-Jan-2021

Correspondence Address:
Thejaswi Dodderi
Nitte Institute of Speech and Hearing, Medical Sciences Complex, Nithyanandanagar, Deralakatte, Mangalore - 575 018, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jnsbm.JNSBM_59_20

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Introduction: The 21st-century lifestyle has swallowing accompanied by competing cognitive activities (texting, reading, and television watching). The potential influence of competing cognitive tasks on swallowing and vice versa is not completely understood. Aim of the Study: This study examined the swallowing and cognitive abilities of healthy young and middle-aged adults in isolated condition and compared their performance with a competing swallow-cognitive dual task. Materials and Methods: Swallowing ability of thirty healthy young adults (20–40 years) and thirty healthy middle-aged adults (41–60 years) were measured by 100-ml thin liquids swallowing, and the cognitive ability was assessed by number recognition task. The two tasks performed in isolation and competing dual-task conditions were observed for changes in: (a) swallowing indices-volume/swallow, time/swallow, and swallow capacity; and (b) cognitive performance-reaction time. Results: Healthy young adults had better swallowing indices and faster number recognition compared to middle-aged adults, in isolated as well as dual-competing condition. Male participants 100-ml swallow capacity was higher, and their number recognition quicker than female participants. Multivariate Analysis of Variance with the main effect of age and gender suggested a statistically significant difference at P < 0.05 in isolated and competing-dual task conditions. Conclusion: Overall, the state of evidence suggests there exists a cumbersome influence of competing cognitive resources on swallowing performance and vice versa.

Keywords: Cognition, number recognition, reaction time, swallow capacity

How to cite this article:
Dodderi T, Umesh L, Hakkeem S. Measuring Effects of Competing Swallowing-Cognitive Task on 100-ml Water Swallowing and Number Recognition: A Crossover Comparative Study in Healthy Young and Middle-Aged Adults. J Nat Sc Biol Med 2021;12:75-83

How to cite this URL:
Dodderi T, Umesh L, Hakkeem S. Measuring Effects of Competing Swallowing-Cognitive Task on 100-ml Water Swallowing and Number Recognition: A Crossover Comparative Study in Healthy Young and Middle-Aged Adults. J Nat Sc Biol Med [serial online] 2021 [cited 2021 Jun 13];12:75-83. Available from:

   Introduction Top

Swallowing is a multisensory stimulating experience. Beginning from perception of food till the completion of sequel events, swallowing is influenced by individual and environmental factors, such as (a) olfaction, to detect food aroma; (b) vision, to capture the visual appeal of the food; (c) proprioception, that enables grasping food from the plate and keeping inside the mouth; (d) audition, to receive internal auditory feedback of sounds while biting and chewing; and (e) cognition, for vigilance, awareness, anticipation, and motivation. All these events are explained under the traditional phases of the swallowing-oral preparatory phase, oral transport phase, pharyngeal phase, and esophageal phase, which is reported to be mediated by the brainstem circuitry and central pattern generator. Swallowing is considered as a temporally linked sequential event that begins from placing the food inside the mouth until the bolus enters the esophagus and reaches the stomach.[1],[2]

Few researchers have also proposed a new swallowing phase that cognates the classic four-stage swallowing model. This new phase conceptualized by Leopold and Kagel[3] was coined as the “Anticipatory Phase of Swallowing.” It is also called as the pre-oral stage of swallowing. This cognitive contributor elucidates the intricate details of a meal like-why we salivate for food?, estimating the bite-size, how quickly we swallow the food, and the role of competing distracters on swallowing.[3],[4],[5]

Lately, curiosity has been brewing in the research community to understand the extent of the relationship between cognition in swallowing and/or vice versa. Researchers have in-depth probed this intriguing question using “Dual-Task Paradigm” – that involves testing two separate tasks simultaneously and comparing its performance with that of the isolation performance.[6] Using this novel concept, clinical studies in Parkinson's disease reported decreased performances in: 5-ml swallow and nonword recognition;[7] as well as 10-ml swallow and digit forward test.[8] In another study, Dodderi and Vaz Larisa[9] measured how swallow indices-volume/swallow (V/S), time/swallow (T/S), and swallow capacity (SC) vary under dual-task condition in 18–24 years healthy young adults. With 100-ml timed test of swallowing and visual feature identification task performance being compared in isolation and in competing condition, the study reported decreased V/S and SC in a longer T/S under dual-task mode. Although the study demonstrated a decrease in swallowing performance, the performance of the cognitive task was not objectively investigated.[10] In another study undertaken by Dodderi, Philip, and Mutum[10] the researchers studied a number recognition task using DmDx software to quantify the attention of the participants. In the swallowing task, 100-ml lukewarm water and 100-ml carbonated sweet water was separately presented in a beaker to derive three swallowing indices. Descriptive statistics revealed that both the swallowing task and the cognitive task performance were below par in dual-task condition compared to the baseline assessment. Collectively evidence supports the literature that changes in swallowing thresholds is dependent on external factors and not just direct sensory cues in the oral-pharyngeal cavity.[5],[11],[12]

According to the Indian Brahmin tradition, mealtime involves consuming food in a disciplined manner without talking. Maintaining silence while swallowing is an important etiquette of dining as it permits the diner to relish the food, correctly chew, and swallow without any risk for choking or aspiration. However, with time traditions have been modified or left out from lifestyle. Undeniably, long past were those days when mealtime comprised giving undivided attention to the food on the plate. An universally observable example of the phenomena is television watching while having meals, with television being the competing cognitive distracter.[13] It's paramount to consider the influence of cognitive distracters on swallowing or vice versa since dual tasking is a common trend in the fast-evolving tech-savvy young generation, in whom the incidence of neurological assaults is steadily increasing.[14]

Swallowing therapy is part of every stroke rehabilitation. Typically, swallowing therapy is provided by applying different therapeutic manoeuvre in conjunction with compensatory strategies and non-oral feeds. The success of these manoeuvres depends not just on the clinician's ability but also on several extrinsic factors. In most of the Indian hospital setup swallowing therapy happens in the general ward which houses multiple beds, and inevitably there are multiple sensory distractions. The possible impact this has on swallowing therapy and its outcome is neglected for practical reasons. In a similar line, there is limited literature on how the cognitive distracters affect the swallowing, in individuals with safe swallowing as well as dysphagia (or swallowing impairment). Hence, the present study is an attempt to investigate performance variations in swallowing indices and cognitive reaction time when 100-ml water swallowing test and number recognition task is performed individually and simultaneously by healthy young- and middle-aged adults.

   Materials and Methods Top

Study design

A comparative crossover study design with nonrandom convenient sampling.


Sixty participants between the age range of 20–60 years participated in the study. The participants were of two age groups consisting of equal Male-Female ratio. Group I (GI) consisted of 30 healthy young adults from 20 to 40 (mean age = 30.31; standard deviation [SD] = 4.55) years and Group II (GII) of 30 healthy middle-aged adults from 41 to 60 (mean age = 50.81; SD = 5.75) years. Participants with a history of glossectomy, medical ailments, head and neck surgery, sensory-motor issues, and neurological impairments did not participate in the study. Cognitive dysfunction was ruled out by administering the Six Item Cognitive Item Test.[15] Participants who scored 7 or higher in the cognitive test were ruled out from the study as it suggested cognitive impairment. The participants of the study also had no risk for swallowing impairment as per the Eating Assessment Tool-10[16] that deems risk for dysphagia if an individual scores 3 or higher. The present study was approved by Institute Ethics Committee. Written consent was taken from participants.


The swallowing task and the cognitive task were administered using the following stimuli.

Swallowing task

The food to be swallowed by the participants was 100-ml thin liquids of room temperature. We chose 100-ml test quantity since the study requires assessment of an individual's natural swallowing style and well documented in literature.[7],[8],[9],[10]

Cognitive task

The cognitive task of the study was a number recognition task. Single-digit(s) from <1> to <9> were used as test stimuli. The test stimuli were further divided into two types: target stimuli, i.e., <1>; and nontarget stimuli, i.e., from <2> to <9>. Selecting <1> as the target stimuli were based on the method of lottery.


Swallowing task

100-ml thin liquids were presented to the participant in a 120-ml capacity transparent disposable paper cup. To maintain consistency of the test volume, the researcher gauzed the test quantity using a commercially available standard measuring cup. This approach was followed for all the tasks.

Cognitive task

Stimuli delivery of the cognitive task was controlled by DmDx[17] software. This freeware was installed in a Toshiba laptop running on Windows 7 edition and programmed to visually deliver the target and nontarget stimuli in the middle of the laptop screen. The stimuli were programmed to present the stimuli in the following order: (1) a <+> sign was displayed for 50-ms to keep the participant vigilant; (2) following this the target or nontarget stimuli, lasting for 1000-ms, was presented on-screen; (3) the cycle was repeated with different stimuli and the inter-stimuli interval (difference between two successive target and/or nontarget stimuli) maintained was 100-ms. This order was followed throughout the cognitive task. The pre-programmed script was loaded and saved in .rtf format. Times New Roman 14 size font was used to present the stimuli in black text color in the middle of the white screen. Responses of the participant were noted by a pre-determined motoric key-press format. Prior to data collection, TimeDx software was run to calibrate the DmDx reaction time calculation.


The study comprised two test formats: (1) baseline assessment and (2) competing dual-task assessment. For our study, the baseline assessment is defined as a task that is performed in isolation and the dual-task is simultaneously performing the two tasks. Every participant underwent a baseline swallowing assessment and baseline cognitive assessment testing. The procedure of the baseline swallowing task, baseline cognitive task, and the competing dual-task are enumerated below.

Swallowing task

Being seated on a chair with backrest and arm support with foot touching the ground, each participant ingested 100-ml lukewarm water under the standard instructions of Timed Test of Swallowing[18] – “You have to continuously swallow the water in your comfortable pace without oral spill-over.” While the participants swallowed, the researcher noted two real-time parameters: (1) the total number of swallow; and (b) total swallowing time.[18] Visual monitoring of hyo-laryngeal excursion and subsequent hyo-laryngeal depression was tallied as one swallow. On the other hand, total swallowing time was calculated by the start of digital stopwatch lap-time once the cup was placed on the lower lip, and the timing ceased on cup withdrawal from the lower lip.

Cognitive task

With the participant being seated comfortably, the laptop was placed on a table at a comfortable height and hand to keyboard distance. The researcher instructed the participant– “Random numbers between <1> and <9> will appear on screen and you need to press key button <1> if the number on screen is <1> and press key button <5> if the number is <2> till <9>. The task must be performed quickly and accurately.” Choice of hand for the keypress was decided by the participant. In participants using the left hand, the key button <1> and <5> was assigned to the little finger and index finger respectively; and for right hand users, it was vice versa (<1> for the index finger and <5> was a little finger). Every participant received a trial set before test run for task familiarization.

Competing dual-task

In the dual-task, participants concurrently performed the swallowing task and the cognitive task. To ensure there is no test preference over either swallowing task or cognitive task, the dual-task was administered under three conditions: (1) dual-task with equal attention to swallowing task and cognitive task; (2) dual-task with more attention to swallowing task and less on cognitive task; and (3) dual-task with more attention to cognitive task and less on swallowing task. Directives to perform the swallowing task and the cognitive task remain unchanged. It was the participant who opted for the hand to hold the cup for the swallowing task and pressing the response button for the cognitive task.

Data analysis

Data across the swallowing task, cognitive task, and the three competing dual-tasks were calculated on an offline basis as follows.

Swallowing task

Data of participants with liquid spillover, in between cessation of swallowing and water residue in the cup were excluded. Using the two real-time data the researcher computed three swallowing indices: (1) V/S, a volumetric data with ml as unit; (2) T/S, a temporal data with second as unit; and (3) SC, a combination of volumetric and temporal data represented by ml/s.[18]

Cognitive task

Responses of number recognition tasks were automatically saved in. exe files by the DmDx software. Error trial (or incorrect response) and lost trial (or failure to respond by pressing the pre-determined key button) was not analyzed.

Competing dual-task

Performance analysis of the swallowing task and the cognitive task of the competing dual-task condition was analyzed in accordance with the format followed for the baseline (or isolation) condition.

SPSS Version 17 (SPSS Inc., Chicago, IBM Corp) was used to analyse the data statistically.

   Results Top

All the participants completed the swallowing, cognitive and competing dual-task as per experiment instructions. There was no drop out of participants. The results of the study are enumerated under the following categories.

Swallowing task


Effect of age

As per the mean data, the results indicate GI participants to have higher volume intake than GII participants. In the temporal index T/S, GI participants swallowed faster than GII, and lastly, GI had higher SC or (swallow speed) speed compared to GII participants. Collectively, GI participants 100-ml water swallowing performance was better than gii.

Multivariate analysis of variance for between GI and GII analysis revealed the following. In baseline task statistical significance was obtained for: V/S (F [1,414.36] = 6.430; P = 0.01); and SC (F [1,394.697] = 6.174; P = 0.01). Similarly, in the competing dual-task with emphasis on swallowing statistical significance was noted for: V/S (F [1,210.636] = 5.069; P = 0.03); T/S (F [1,1.285] = 4.601; P = 0.04); and SC (F [1,145.291] = 5.282; P = 0.02). In the competing dual-task with an emphasis on the cognitive task and dual-task with equal emphasis on swallowing and cognition, there was no statistically significant difference. Pairwise comparison by Bonferroni post hoc analysis is tabulated in [Table 1].
Table 1: Pairwise comparison by Bonferroni post hoc analysis for effect of age on swallowing task

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Effect of gender

Comparing the test results, the study reveals that male participants had better swallowing skills compared to female participants. The general trend observed was, male participants had higher V/S, quicker T/S, and overall increased SC. Mean with the SD of V/S, T/S, and SC of males and females of GI and GII are depicted in [Figure 1],[Figure 2],[Figure 3], respectively.
Figure 1: Mean values of volume/swallow index

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Figure 2: Mean values of time/swallow index

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Figure 3: Mean values of swallow capacity index

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MANOVA test suggest a statistical significance for gender only for baseline V/S (F [1,610.751] = 10.423; P = 0.03) and baseline SC (F [1,785.060] = 14.713; P = 0.001). No statistical significance was observed for any other test conditions. Post hoc analysis was done using the Bonferroni test, and the results are tabulated in [Table 2].
Table 2: Pairwise comparison by Bonferroni post hoc analysis for effect of gender on swallowing task

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Swallowing task


Repeated measures of ANOVA were tested for observing any within-group statistical difference. In GI participants, we observed statistical significant difference for: V/S (F [3,428.618] = 22.762; P = 0.000); T/S (F [3,3.581] = 10.446; P = 0.000); and SC (F [3,629.820] = 38.683; P = 0.000). Post hoc analysis was done using Bonferroni test and the statistical significance values for V/S, T/S, and SC are tabulated in [Table 3],[Table 4],[Table 5], respectively. On the continuum in GII participants, we observed statistical significant difference for: V/S (F [3,106.472] = 7.518; P = 0.000); T/S (F [3,2.94] = 11.857; P = 0.000); and SC (F [3,190.325] = 14.683; P = 0.000). Post hoc analysis was performed using Bonferroni test and the statistical significance values for V/S, T/S, and SC are tabulated in [Table 6],[Table 7],[Table 8], respectively.
Table 3: Pairwise comparison by Bonferroni post hoc analysis within Group I for volume/swallow index

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Table 4: Pairwise comparison by Bonferroni post hoc analysis within Group I for time/swallow index

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Table 5: Pair wise comparison by Bonferroni post hoc analysis within Group I for swallow capacity index

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Table 6: Pair wise comparison by Bonferroni post hoc analysis within Group II for volume/swallow index

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Table 7: Pair wise comparison by Bonferroni post hoc analysis within Group II for time/swallow index

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Table 8: Pair wise comparison by Bonferroni post hoc analysis within Group II for swallow capacity index

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Cognitive task


Effect of age

Results of the study suggest GI participants identification of the target and nontarget stimuli to be faster than GII participants. This was observable in both baseline and competing dual-task conditions.

Postanalysis, statistical significant results of MANOVA for the target stimuli was: (F [1,99123.09] = 7.571; P = 0.02), for baseline task; (F [1,36313.769] = 8.282; P = 0.02), for dual task with emphasis on cognitive task. Similarly for the nontarget stimuli statistical significant values were: (F [1,782000.960] = 11.323; P = 0.01), for baseline task; and (F [1,50076.122] = 5.265; P = 0.05), for dual task with emphasis on swallowing and cognitive task. Pair wise comparison by Bonferroni post hoc test statistical significant values of target and nontarget stimuli are tabulated in [Table 9] and [Table 10] respectively.
Table 9: Pair wise comparison by Bonferroni post hoc analysis for effect of age on a cognitive task (target stimuli)

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Table 10: Pair wise comparison by Bonferroni post hoc analysis for effect of age on a cognitive task (nontarget stimuli)

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Effect of age (make it into sub-heading style). Faster reaction time was noted in male participants over female counterparts in GI and GII for identification of target and nontarget stimuli. Mean and SD of the target and nontarget stimuli is depicted in [Figure 4] and [Figure 5] respectively.
Figure 4: Mean values of cognitive task (target stimuli)

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Figure 5: Mean values of cognitive task (nontarget stimuli)

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Multivariate analysis of variance was applied with gender as the variable. Results indicate no statistical significant difference between males and females for both target and nontarget stimuli.

Cognitive task


Repeated measures of ANOVA test results suggest no statistically significant difference in GI and GII participants for target and nontarget stimuli.

   Discussion Top

In the present study, we compared baseline swallowing and cognitive task performance with competing dual-task performance in healthy young and middle-aged adults. Results obtained in the study revealed GII participants had poor swallowing indices and longer reaction time in isolation task condition and competing dual-task when compared to GI. Such inhibitory performance by GII participants can be due to poor oro-motor control and decreased cognitive flexibility observable with an increase in age.[8] In baseline swallowing, studies enumerate that young adults hold the upper hand in swallowing due to differential oro-pharynx anatomy thereby allowing the younger participants to have better swallowing skills compared to older participants.[19] On the continuum, a decrease in baseline cognitive performance by GII participants suggests inability in the healthy middle-aged adults to process the sensory information fast and allocate necessary resources to take the right decision by means of key press reaction time.[20]

In the competing dual-task condition, it was interesting to note that both GI and GII had a decrease in performance across swallowing and cognitive tasks. The works of Pashler,[21] conceived as “The Capacity Sharing Model” helps us understand the reason behind this decrease in performance. As per the model, attention is a limited mental ability that functions as per the resource allocated to each task. Considering this, we understand that in competing for dual-task conditions there would have been poor resource allocation to either of the task resulting in decreased SC and longer reaction times. Earlier works refer to this phenomenon as the “Bottleneck effect” that arises from the competition for the shared resources between the swallowing and cognitive task. The study results are supportive of literature.[8],[9],[10]

Drawing parallel the results of our study with findings of Dodderi and vaz Larisa,[9] their study reported performance of healthy young adults V/S, T/S and SC: in baseline condition to be - 19.71-ml, 1.25-s and 15.92-ml/s respectively; and performance in dual-task condition to be - 14.33-ml, 1.61 s, and 9-ml/s respectively. Similarly, in another study, Dodderi, Philip, and Mutum[10] reported higher V/S of 12.07-ml for baseline tasks compared to 8.72-ml for dual-task conditions during water swallowing; and 14.01-ml and 9.28-ml for the same swallowing index for swallowing carbonated water. Dual-task condition demanded longer T/S of 1.42-s and 1.31-s compared to isolation task, which required lesser time of 1.18- and 1.2-s for swallowing water and carbonated sweet water, respectively. Finally, SC of the study reported for isolation condition was 10.5-ml/s and 12.17-ml/s; and 6.99-ml/s and 7.56 ml/s for dual task. In the reaction time paradigm, participants' baseline reaction time was 485.27-ms. In the dual-task condition, the participants took 432.9-ms and 503.83-ms for water and carbonated sweet water condition, respectively.

The present study has its limitations. Foremost, participant's handedness was not controlled when the dual-task was performed; while few subjects used the right hand for holding the cup and left hand for keypress the rest were vice versa. Recently, using behavioral experiments Balasubramanium, et al.[22] reported cerebral hemispheric laterality for swallowing, with left hemisphere being dominant for quantitative measures V/S and SC; and the right hemisphere is dominant for temporal measure T/S. Thus, inconsistency in the participant's handedness may have influenced the study results. Second, the test quantity of the study is 100-ml, which reflects sequential swallowing ability and hence the present study findings are confined to large test quantity and cannot be generalized to smaller test quantity, which assesses single sip swallowing skill. Further, the application of the study is restricted to thin liquids.

   Conclusion Top

Based on the results of the present study, we conclude that performing swallowing and cognitive tasks are not advisable in healthy young and middle-aged adults. The resultant effect that arises from performing a competing dual-task is a compromised swallowing and cognitive performance. This has clinical implications in the swallowing assessment and rehabilitation and cautions all dysphagia practitioners to control inherent distracters in the clinical setup. Further studies are warranted in the geriatric population who are prone to presbyphagia (age related swallowing impairment) and age related decline in cognition skill.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]


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