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Purpose
The Coffee Task is a validated functional assessment that quantifies the performance of myoelectric, multi-articulating upper limb prosthesis control (Lee et al., 2024).
About the Coffee Task
The Coffee Task is a representative bilateral activity of daily living (ADL), during which individuals simulate brewing a cup of coffee with a pod-style coffee maker using 3 functional grasps (fist, pinch, point) and 5 transitions between these functional grasps. A grasp transition can be achieved in many ways depending on the control approach of the prosthesis (e.g., trigger control, manual, pattern recognition, RPNI, etc.).
The task was designed as an objective assessment tool that enables quantification of performance during grasp transitions - number of errors and completion time - in users of multi-articulating upper limb prostheses. No other assessment are known to exist that assesses prosthetic grasp selection performance.
There are two versions of the task: segmented and continuous.
Segmented Task: Individuals are asked to attempt each of the 5 segments of the task until all parts of the segment, including a successful grasp transition, are completed. They receive up to 5 attempts per segment to complete, leaving the maximum accumulated error of 25 for the full task.
Continuous Task: Individuals are asked to complete the full task continuously as fast as they can while using as many correct grasp transitions as possible. They are not allowed to complete parts of the task designed to be completed by the prosthetic hand with their intact hand (dominant hand for those with bilateral amputation). Individuals receive up to 2.5 minutes to complete the task.
Materials Needed:
Pod-style coffee maker with a small push-to-start button
2 beads
1 small cup that can fit under the coffee maker
Reusable coffee pod
Sugar packets
Sugar packet holder
Container for sugar packet trash
Video camera for scoring errors (segmented)
Stopwatch for timing (continuous)
Materials Placement:
All materials are laid out on the table whose height aligns with the participant’s anterior-superior iliac spine. The participant completes all tasks standing in front of the table.
The coffeemaker is placed on the contralateral side of the prosthesis approximately aligned with the shoulder.
The cup is filled with the two beads and is placed on the ipsilateral side of the prosthesis, aligned with the shoulder.
The trash container is placed laterally to and behind the cup.
Sugar packets should be in a holder and aligned with the midline of the participant between the cup and the coffeemaker.
The reusable coffee pod is also aligned with the midline of the participant, in front of the sugar packets, closer to the participant.
Place a video camera in front of the participant for scoring the number of errors. The camera should capture the entire set-up and participant.
Coffee Task Demonstration
Scoring the Segmented Version
Errors are defined as any user or software error between "go" and the end of the segment. Errors are dependent of the prosthetic control approach.
Trigger Control Errors:
(direct, cycling, gyroscope doesn't use myo signals)
Grasp Error: User applied the correct trigger for the intended grasp, but the hand transitioned to an unintended grasp.
No Response Error: User applied the correct trigger for the intended grasp, but no grasp transition occurred.
User Error: User applied the incorrect trigger for the intended grasp, and the hand transitioned to the unintended grasp (correct trigger pairing).
User & Software Error: User applied an incorrect trigger for the intended grasp, but the hand transitioned to the intended grasp (incorrect trigger pairing).
Mid-Attempt Hand Open Error: Hand opens/flutters without user input.
Mid-Attempt Grasp Error: User does not apply a trigger, but the hand transitions to an unintended grasp.
Non-Transition Error: Dropping objects without opening the hand.
Pattern Recognition Errors:
Commanded Decode Classification Error: User applies transition, but the hand transitions to unintended grasp.
Commanded Software Error (No Response): User applies transition, but no grasp transition occurs.
Un-Commanded Mid-Attempt Grasp Selection: There is no intended action, but the hand transitions to an unintended grasp.
Un-Commanded Mid-Attempt Hand Open: Hand opens/flutters without user input.
Non-Transition Error: Dropping objects without opening the hand.
Helpful Tips:
During Fist/Power/Cylindrical segments, if the prosthesis is grabbing the cup with just the thumb, index, and middle fingers (i.e., the fourth and fifth fingers do not curl around the cup), this would be considered an error as the prosthesis is in a version of the Pinch grip.
Literature
Lee, C., Vaskov, A. K., Davis, A. J., Kartes, J. M., & Gates, D. H. (2024). Development and validation of the coffee task: a novel functional assessment for prosthetic grip selection. Journal of NeuroEngineering and Rehabilitation, 21(1), 21. https://doi.org/10.1186/s12984-024-01307-y
Lee, C., Vaskov, A. K., Gonzalez, M. A., Vu, P. P., Davis, A. J., Cederna, P. S., ... & Gates, D. H. (2022). Use of regenerative peripheral nerve interfaces and intramuscular electrodes to improve prosthetic grasp selection: a case study. Journal of neural engineering, 19(6), 066010. https://doi.org/10.1088/1741-2552/ac9e1c
Questions? Contact Us!
Mira Mutnick
mmutnick@umich.edu
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