So 1976 gives us support to request team interpreting or at the very least, switching interpreters for assignments of one hour or longer. No other studies specifically investigating assignment duration and interpreter fatigue were conducted until Gabrian and Williams published their 2009 research "The Effect of Interpreter Fatigue On Interpretation Quality"
The 2009 study was conducted at Gallaudet University. The researchers were able to recruit a single subject and chose a case-study approach. The subject was video recorded interpreting two different extended source texts (80+ minutes each); one was an ASL source text interpreted into English, the other an English source text interpreted into ASL. Because of the overwhelming amount of data it was reduced to four discrete five-minute segments for each task (ASL-to-English and English-to-ASL): from 10 to 15 minutes; from 30 to 35 minutes; from 50 to 55 minutes; and from 74 to 79 minutes (due to avoiding a change from monologue to dialogue during a question-and-answer session at the end of a lecture).
Both the ASL to English and English to ASL samples demonstrated deterioration of the message over time as measured through OMISSIONS. The interpretation into ASL showed a gradual increase in omissions across all four segments. The interpretation into English showed a constant rate for the first three segments followed by a dramatic increase in the final segment.
CONCLUSION - The research conducted by Gabrian and Williams support the general conclusions that Brasel had found: That sustained interpretations show signs of deterioration by 30 minutes and the quality is more seriously diminished after one hour.