ET Program Design. The ET program is based on the hypothesis
that a substantial contributor to ARCD is negative plasticity,
learning driven changes in brain function in response to decreased
brain use conditions and increased noise conditions that
lead to reduced accuracy and speed of processing in brain
representations of sensation, cognition, memory, and motor
control and decreased function of neuromodulatory systems that
control learning and memory (17). In this initial form, the
program consisted of six exercises designed in aggregate to
reverse these dysfunctions by improving representational fidelity
in auditorylanguage systems and very intensively stimulating
neuromodulatory structures throughout hour-long training sessions.
The exercises adaptively progressed in difficulty, beginning
with relatively easy task forms and progressively advancing
in the listening accuracy challenges they presented as a user’s
abilities improved.
The first of the six exercises required users to reconstruct the
identity (upward or downward) and sequence of frequencymodulated
sweeps. The task progressed by changing the duration
and interstimulus interval between the sweeps. The second
exercise required users to identify a synthetically generated
syllable (e.g.,ba) from a confusable pair (e.g.,bavs.da).
The task progressed by changing the duration and intensity of the
sweep component of the initial consonant. The third exercise
required users to match short spoken confusable consonant–
vowel–consonant words (e.g., bad, dad) from a spatial grid. The
task progressed by changing the number of potential matches
and processing the spoken speech in a manner similar to
Nagarajan et al. (40) to stretch and emphasize rapid transitions.
The fourth exercise required users to reconstruct a sequence of
short spoken words (identical to the third exercise stimuli). The
task progressed by changing the number of words in the sequence
and the level of speech processing. The fifth task
required users to reconstruct a spoken series of instructions by
using the computer mouse to click and drag icons on the
computer screen. The task progressed by changing the number
and complexity of the instructions and the level of speech
processing. The sixth task required users to answer questions
regarding short narratives. The task progressed by changing the
length of the narratives and the level of speech processing.
Stimuli across the exercises were chosen such that they
spanned the acoustic and organizational structure of speech,
from very simple acoustic stimuli and tasks (e.g., time order
judgments of rapidly successive frequency modulated sweeps) to
the complex manipulations of continuous speech (e.g., narrative
memory). In each case the progression of the exercise was
governed by the user’s individual performance during a training
session. As a user performed trials correctly, the difficulty level
was increased, and as a user performed trials incorrectly, the
difficulty level was decreased.
This training approach is described as brain plasticity-based
training because the exercises are designed to induce brain
plasticity by engaging mechanisms that have been directly shown
in other work to lead to and promote brain plasticity (e.g., refs.
10 and 41–43).