Can the reaction time in gait initiation be influenced by emotional ascendancy, elicited by both visual and auditory stimuli in healthy subjects between 18 and 35 years?
Emotion, according to Merriam Webster the definition of emotion is “a conscious mental reaction (such as anger or fear) subjectively experienced as strong feeling usually directed toward a specific object and typically accompanied by physiological and behavioural changes in the body”.
Retrieved from: https://www.merriam-webster.com/dictionary/emotion; 7th February 2019.
Intuitively you would expect if you desire a specific object, you tend to move towards what you desire. Much research investigated the psychophysiological response on manipulated facial expressions. They found particularly in electroencephalographic (EEG) asymmetries over the frontal cortex. Positive emotions (e.g. joy or happiness) are related with a relatively greater left frontal cortical activation. Contrarily, negative emotions (e.g. sadness or angriness) are associated with relatively greater right frontal activation. This asymmetry has given way for the approach and avoidance behaviour model (Coan & Allen, in press; Davidson, 1993, 1998; Harmon-Jones & Allen, 1997, 1998; Sutton & Davidson, 1997). According to this hypothesis, the left hemisphere differentially specializes in approach motivation, whereas the right hemisphere differentially specializes in avoidance motivation (Harmon-Jones et al. 2010).
Approach and avoidance behaviour have been studied in several ways. The main outcome measure is reaction (or: initiation) time, i.e. “the period of time between the detection of a stimulus at a sensory receptor and the performance of the appropriate response by the effector organ” (“reaction time.” A Dictionary of Biology.
Retrieved February 15, 2019 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/reaction-time-1).
In most related experiments, visual stimuli have been used to encourage emotional states. These stimuli are typically selected from the International Affective Picture System (IAPS; Lang et al., 2005) and involve pictures varying in valence (pleasantness) and arousal, based on the assumption that emotions can be classified along these two dimensions (Lang et al., 2005). When a positive stimulus is exhibited, such as happy faces, participants are predominantly faster at making approaching movements compared to avoiding movements. This reflects an intuitively approaching tendency towards a positive evaluated stimulus. Comparatively, when a negative stimulus is exhibited, such as angry faces, participants are faster at making avoiding movements compared to approaching movements. This reflects an intuitively avoidance tendency towards a negative evaluated stimulus. The latter is in line with other studies who have found faster and more accurate reactions in the congruent condition than the incongruent condition, where participants had to override their ‘‘intuitive’’ action tendencies (Roelofs et al. 2009a).
Likewise the visual system, in the auditory system, the primary route from the periphery to the brain is crossed (Moore, 1987). While ipsilateral, ear to brain pathways exist, performance on tasks involving auditory stimuli presented to the right ear primarily reflects processing in the left hemisphere and vice versa, due to the strong crossed pathways between the ear and the auditory cortex. Komeilipoor et al. (2013) used transcranial magnetic stimulation (TMS) to clarify how non-verbal emotionally characterized sounds modulate the excitability of the corticospinal motor tract (CST). Unpleasant stimuli resulted in a significantly higher facilitation of motor potentials evoked in the left hemisphere (avoidance), while pleasant stimuli yielded a greater CST excitability in the right one.
During quiet standing, stability requires that the vertical projection of the center of mass falls within the base of support[10,11]. The center of mass corresponds to the point where the mass of the whole body is concentrated. It is the point of application of the gravity force vector, i.e. center of pressure (COP). In the standing posture, the base of support refers to the area that includes every point of contact that the foot (or the feet) make(s) with the supporting surface.
Gait initiation (GI) is transition from quiet standing to walking. During GI precise control of the COP is required for an accurate acceleration of the COM in the desired direction (Yiou, Caderby, Delafontaine, Fourcade & Honeine, 2017).
Gait initiation is classically divided in three successive phases: a postural phase which precedes the swing heel off (this phase corresponds to the so-called anticipatory postural adjustments (APAs), followed by the foot lift phase that ends at the time of swing toe clearance (the mass of the body is transferred to the stance leg during this phase), and finally an execution phase that ends at the time of swing foot contact with the supporting surface.
It has been widely reported that emotional states are reflected in the center of pressure (COP) trace, and can influence gait initiation parameters like velocity, step length, and reaction time (e.g., Gélat et al., 2011; Naugle et al., 2011; Stins and Beek, 2011; Stins et al., 2015).
The main goals of the current research (1) difference RT congruent vs. incongruent in GI determined with COP, (2) if sound in either the right or left ear influences the RT in GI determined with COP.
The preliminary research question
The preliminary research question is as follows:
Can the reaction time in gait initiation be influenced by emotional ascendancy, elicited by both visual and auditory stimuli in healthy subjects between 18 and 35 years?
Method
2.1 Participants
The age ranged from 18 to 35 years. A written informed consent was obtained from each participant.
2.1.1 Inclusion and exclusion criteria
Inclusion Exclusion
Age > 18 – 35 years Any peripheral or sensory disorder*
Diagnosed neurologic disorder that could affect RT*
Any orthopaedic or musculoskeletal dysfunction*
Table 1: inclusion and exclusion criteria
* Bryssinck, J. (2017). REACTION TIME IN POSTURAL CONTROL DURING AGEING (doctoral dissertation, Ghent University).
2.2 Materials and methods
The posturographic data will be recorded using a 1 m x 1 m strain gauge force plate with a sampling frequency of 100 Hz. The force plate contains eight sensors; four for measuring the forces in the z direction, and two sensors for the x and y directions. The collected data will be converted to the total force in three directions( Fx, Fy and Fz). Subsequently the moments will be calculated, and the Center of Pressure (COP) will be calculated from the Mx and My vectors. The COP represents the position of the COM, projected along the z-axis (i.e. the ground reaction force of this particular point (Brenière, Cuong Do, & Bouisset, 1987)).
During the test the participant will be wearing a headphone. Auditory stimulation will be elicited by a tone in either the left or right ear. There will be no difference in pitch
Subsequently, images will be shown on a 55-inch monitor placed 30 cm in front of the participant at eye-level. The image size is 32 × 43 cm, so that it was completely visible while standing close to the screen. There will be two photodiodes attached to the monitor for detection of the tone-onset and image onset and offset. These offsets will be synchronized with the force plate recording. This process won’t be visible to the participant. The visual stimuli are chosen from the IAPS (Lang et al., 2005). Only high-arousal pictures will be used since previous research showed that especially these pictures have discernible impact on gait initiation (Stins et al., 2015a, 2015b).
Two picture categories will be used: (1) happy (high arousal pleasant) and (2) angry (high arousal unpleasant). Twenty unique pictures were chosen from each picture category. The test contains 4 blocks 20 pictures.
2.3 Procedure
After having signed the informed consent form, the participants will be divided in two groups. The participants with an even number will get the congruent instructions; the participants with an odd number will get the incongruent instructions. In the congruent group the participant will be instructed to step forward when a happy face appears, and to step backward when an angry face appears. The opposite applies to the incongruent group. They will be instructed to step forward when seeing an angry face, and step backwards whilst seeing a happy face. No instructions on step length and speed will be given. All steps will be initiated with the right leg.
After this instruction participants have to step onto the force plate. They will be instructed to touch a piece of grey tape, which will be attached in the center of the force plate, with their heels, to ensure that the participant will be able to make a similar step size in both forward and backward direction. From this position, participants have to either initiate a step forward or backwards with the right leg. A 4-trail practice session precedes the experiment in the first block; in the following blocks only a 2-trail practice session will be preceded.
Each trail starts with the instruction, after the instruction a fixation cross appears in the middle of the screen. The participant will get the instruction to focus on the cross as long as it is shown on the screen. Meanwhile, a beep will be played in either the left or right ear. The participant can neglect this sound. Subsequently, one of the IAPS images appears.
After each step the participants have to wait for an instruction to appear on screen. This instruction contains that the participant is allowed to resume to their original position. Subsequently, the participant has to wait for a new trial. The cue for GI was the onset (i.e., appearance) of the stimulus.
The tone side will be randomized; also all 80 IAPS images will be presented in random order, with a break of a self-chosen length after every 20 trials.
Our paradigm involving at least 2 s viewing duration allows us to assess whether emotional content interfered with this process of parameterization and execution of the motor program, as evidenced by the COP profile. This paradigm has been used in previous research (Bouman et al., 2015; Naugle et al., 2011; Stins et al., 2015a, 2015b), all involving forward GI.
2.4 Data reduction
The raw data will be analysed using MATLAB.
2.4.1 Reaction time
The reaction time was determined as the time interval between picture offset (cue for GI) and the time at which the force in the anterior or posterior direction exceeded 5 N (Bouman et al., 2015).
2.4.2 APA amplitude
To maintain equilibrium during GI, the central nervous system (CNS utilizes anticipatory postural adjustment (APAs) by pre activation of the trunk and leg muscles prior to initiation of a movement, in this study this will be GI. This results in a small displacement in COM, and therefore COP. Belenkiy et al. 1967; Massion 1992; Aruin and Latash 1995; Li and Aruin 2007).
This adjustment is the first period that can be recognized when unfolding GI. The shape and timing depends on the direction in which the body will be accelerated with respect to the command (i.e. direction of GI). (Lepers & Brenière, 1995).
In the present study, the APA is the magnitude in anterior-posterior (AP) direction between the initial position of the COP and the most anterior and lateral displacement of the COP in the direction of the right leg (Naugle et al., 2011).
2.4.3 Peak velocity
Peak velocity of the COP will be determined in the AP – medial lateral (ML) plane. This will be established by a numeral differentiation of the position of the COP. Usually, the peak velocity is reached when the largest weight shift occurs. This will be when the stance leg and the swing leg are both on the plate (Bouman & Stins, 2018).
2.4.4 Step length
The difference along the y- axis between the initial position of the COP and the final position of the COP after completing the step (Bouman & Stins, 2018)
2.4.6 Gender
We did not separate the scores for males and females, as previous research has found that gender does not influence kinematic parameters (Naugle et al., 2011).
2.5 Statistical analysis
A block contains 20 trails.
Firstly, in the first block, the first four trails and in the following blocks the first two trails will not be analysed since these trails are try-outs.
Secondly, the incorrect trails are identified and deleted. A trail is incorrect when (Bouman & Stins, 2018):
– A step is made in the wrong direction n
– A step is made with the left limb
– The RT falls outside the range 250-2000 ms
– Participant fails to adopt to adopt a quiet standing posture prior to the stimulus, defined as COP velocity [10 cm/s, or (e) participants do not come to a complete standstill following step execution.
For the congruent and incongruent group, if a normal distribution is found, an independent t-test will be used to determine if there is a significant effect in RT for each direction. This contains forward for congruent happy group and incongruent angry group, and backwards for congruent angry group and incongruent happy group.
Four dependent GI variables (RT, APA, peak velocity, and step length) will be analysed in IBM SPSS (version 24) using a 3-way (movement direction: forward vs. backward), X 2 (emotion: happy vs. angry facial expression), X 2 (auditory: left vs. right tone) multivariate repeated measures analysis of variance (RM MANOVA) to control for type-I error, since these dependent measures are potentially related (see Naugle et al., 2011; Stins et al., 2015a, 2015b).
If there is a significant distribution between the blocks, a dependent t-test will be used to determine which block is significantly different.
2.6 Hypothesis
Based on the latter literature the expected main effect between the groups will be:
– Congruent stepping gives a shorter RT compared to incongruent stepping
Furthermore, the interaction effect within the groups will be:
– In the congruent group: a happy face combined with a beep in the right ear and with an angry face combined with a beep in the left ear will give shorter a shorter RT than the group with a happy face combined with a beep in the left ear and an angry face combined with a beep in the right ear
– In the incongruent group: a happy face combined with a beep in the left ear and with an angry face combined with a beep in the right ear will give shorter a shorter RT than the group with a happy face combined with a beep in the right ear and an angry face combined with a beep in the left ear