Procedure

During the first part of the experiment, participants performed each of the four experimental conditions involving the production of the tasks in isolation (simple speech, verb generation, math addition and motor tracking). Each task utilized 15 instances for data collection; 15 sentences repeated, 15 math questions, and 15 nouns presented. The order of these tasks was counterbalanced across all participants. Once these four tasks had been completed, the participant performed three experimental conditions (concurrent speech + cognitive, concurrent speech + linguistic, and concurrent speech + motor) involving concurrent tasks. The order of these three concurrent experimental conditions was randomized across the participants.

2.4.1 Experimental Conditions

Condition 1: Simple Speech Task. The speech task consisted of the repetition of a carrier phrase. Each participant was asked to repeat the carrier phrase “The next word I

am going to say is peach” 15 times consecutively, prompted by the sound of a beep for each repetition.

Condition 2: Math Addition Task. The math addition task consisted of 15

mathematical questions. The participant was presented with a mathematical addition question on a computer display and asked to verbally respond with the correct answer. The questions increased in difficulty after every set of 5 problems, beginning with 5 single digit - single digit addition questions (3+3), followed by 5 double digit - single digit addition problems (52+8), and finally, with 5 questions of double digit - single digit - single digit addition questions (42+4+7).

Condition 3: Verb Generation Task. In the verb generation task, the participant was presented with a written representation of a noun on a computer display and requested to verbally report a verb action that could be associated with the presented noun. For example, the participant, presented with the noun “book”, may have responded with the verb action “read”. Fifteen different nouns were displayed in succession, varying in degree of difficulty on two different levels, association and selection, to create a

hierarchy of three levels of difficulty; strong association-large selection such as “music”, strong association-low selection as for the noun “cup”, and weak association-low

selection such as for the word “button”. The nouns were presented in the following order: 5 nouns of strong association-low selection presented first, followed by 5 nouns designated as strong association-high selection, and finally with 5 nouns delineated as weak association-high selection.

Condition 4: Motor Task. The motor task involved a visual-motor tracking task using a standard hand-held blood pressure test bulb attached to an air pressure transducer system. The participant was required to track a continuous vertical sinusoidal target signal on an oscilloscope-like display by increasing and decreasing the pressure exerted on the hand bulb. The sinusoidal target appeared as a horizontal band (5mm) moving rhythmically and vertically across the mid-portion of the screen. The manipulation of the hand bulb was translated onscreen as the rising and falling of a moving horizontal line. The tracking task required the participant to keep the horizontal line (associated with their hand

pressure) in the center of the continuously moving horizontal band (sinusoidal target). The difficulty of the task was increased twice throughout the task by increasing the speed of movement for the horizontal band (sinusoidal target). Each tracking trial lasted

approximately 24 seconds and was initiated when the participant’s performance was observed to normalize. The initial speed was set to 0.25Hz, followed by an increase to 0.5Hz, and the final phase which consisted of the band moving at a speed of 0.75Hz.

Condition 5: Concurrentspeech + cognitive task. The participant performed the math addition task concurrent with the simple speech task. In this concurrent condition, the participant would solve mathematical addition equations while repeating the carrier phrase “The next word I am going to say is ____”. Once the participant had determined the answer to the question, the participant would respond with their answer, inserting it at the end of the carrier phrase. For example, if displayed with the question “3 + 3”, the participant would respond “The next word I am going to say is 6”. The display of each question was signaled with a tone, prompting the participant to begin by saying the carrier phrase and solving the question. Each trial lasted as long as necessary for the participant to provide their best guess at the correct answer for the mathematical addition equation.

Condition 6: Concurrent speech + linguistic task. Each participant performed the simple speech task and the verb generation task concurrently; in which they performed the verb generation task while repeating the phrase “The next word I am going to say is ____”. In this concurrent task, the participant would insert their verb action response at the end of the carrier phrase. For example, if the participant was presented with the noun “cup”, they might respond “The next word I am going to say is drink”. Each trial lasted as long as necessary for the participant to either provide an answer, or indicate that they could not originate one. The presentation of the noun commenced with a short beep, notifying the participant that the trial had begun and to begin repeating the carrier phrase while formulating their answer.

Condition 7: Concurrent speech + motor task. The participant performed the simple speech task and the motor task concurrently. The participant manipulated the hand-held

pressure bulb while tracking the onscreen sinusoidal target signal and repeating the original carrier phrase, “The next word I am going to say is peach”. The original carrier phrase was repeated 5 times at each tracking speed, with each repetition prompted by the sound of a short beep. After the participant had completed repeating the carrier phrase 5 times, the tracking speed was increased and the task repeated at the faster speed.