Background on Brasel's (1976) study
Barbara Babbini Brasel (B3) conducted her research at CSUN. Her research was published in 1976 as part of a Center on Deafness Publication Series (1976 was the first year of the publication series). Brasel's study was the fourth article in the section titled "USE OF INTERPRETERS". The fifth article, however, mentions the exact same title - "The Effects of Fatigue on the Competence of Interpreters for the Deaf" in its bibliography, but provides a publication date of 1969 (and also identifies the source as "San Fernando Valley State College" - the former name of the place now known as the California State University at Northridge). This means that the 1976 publication date actually refers to research conducted in the 1960s, no later than 1969.
Within the 1976 publication there are references to information "that will be discussed later in this paper", but no subsequent discussion occurs. It is this researcher's assumption (educated guess) that the 1976 publication was actually a summary of the original 1969 research rather than a complete reproduction of it.
The original study involved five subjects (three female, two male) but one (male) was eliminated from portions of the study due to insufficient interpreting skills. Each subject's skills were evaluated using a 13-item evaluation tool (not revealed in the study's 1976 publication) that rated skills based on five minutes of interpreting work. who interpreted different lengths of lecture content (pre-recorded on audio tape): 0 minutes (control subject), 20 minutes, 30 minutes, 60 minutes and 90 minutes.
The 1976 publication clearly identifies that the control subject was female and that her skills were evaluated differently (based on her participation in a separate study that had used the same evaluation tool). This leaves two female and two male interpreters for the remainder of the study. Of all five subjects Brasel indicates that three had "good/outstanding skills," one had "acceptable skills" and one had "high unacceptable skills". Further description in the 1976 publication reveals that the 60-minute and 90-minute interpreters had "good/outstanding skills" and that the insufficiently-skilled interpreter performed for 20 minutes. Thus the resulting table can be created:
0 minutes (control) - good/outstanding OR acceptable skills
20 minutes - high unacceptable skills
30 minutes - good/outstanding OR acceptable skills
60 minutes - good/outstanding skills
90 minutes - good/outstanding skills
It is worth noting that this research was not exclusively related to the duration of interpreting assignments and interpreter fatigue. The study actually had several other assessments including a trigram test, a math test and a typing test. The trigram test involved revealing ten cards with three-letter sequences for 3-second intervals followed by the subject writing down as many trigrams as they could remember. The math test required subjects to correctly add a column of ten three-digit numbers. The typing test allowed subjects five minutes to re-type a source (typed) text. Each subject completed all of these assessments prior to their interpreting task, thus the need for the control subject to account for test/te-test effects.
As with any study the low number of subjects gives room to doubt the general applicability of the results to the general population. The study is still useful, however, because it sheds light on the question of assignment duration related to interpreter fatigue.
The evaluation of interpreter fatigue affecting the interpretation itself was accomplished using a four-person panel of two Deaf evaluators (Brasel being one of them) and two skilled Interpreter evaluators. Deaf judges looked for errors (mis-articulation, semantic mismatch, omissions) and also noted any time that they felt "baffled or confused or did not understand a fingerspelled or signed word". The Interpreter judges focused on omissions, substitutions, or other skewing where the source and target texts did not match. Duration of the interpretation was divided into 5-minute segments by a time-keeper, visible to the judges but behind the subject who indicated five-minutes, ten-minutes and so forth.
There are several points to notice about the study. First, there was no video recording made of the interpreting performances. All evaluation was accomplished by the written comments of four panel members watching the live performance. The second point to consider is that the subjects had live audience members watching their work, but every time they wrote something down, it was to note an error (negative feedback). Third, the source text is an audio recording that cannot be stopped or interrupted for clarification. The speaker is not physically present and no visual aids (gestures, notes, pictures, etc) accompany the source message.
The most significant results that Brasel reports are that "for up to 30 minutes, there are no significant differences in interpreting competence, errors or quality –– although a deterioration can be noted beginning at about 25 minutes. After 30 minutes there is a slow but steady increase in error rate and after 60 minutes this increase becomes significant." In other words, we can interpret 30 minutes without significant deterioration in the message (but fatigue is noticeable at about 25 minutes). Interpreters can only work about an hour before their work begins to significantly suffer.
These results largely depend on the interpretations generated by the two subjects who worked longer than 30 minutes.