## 4 Results and Discussions
### Eye Tracking and Keystroke Logging Data Analysis
The presence of substantial outliers in TT processing, with some gaze durations exceeding 6000 ms (E-C) and 20,000 ms (C-E), suggests that certain translation segments require significantly more cognitive effort, possibly due to lexical retrieval challenges, decision-making processes, or syntactic complexity. These findings also support the necessity of including an interaction term between gaze event duration and AU type in the statistical models. Given that gaze event duration appears to influence pupil dilation differently depending on the processing condition, failing to model this interaction could overlook  
Figure 4: Gaze event duration by participant. Figure 7 illustrates the relationship between pupil dilation and gaze event duration for both English-to-Chinese (E-C) and Chinese-to-English (C-E) translation directions. The blue curve in each scatterplot represents a smoothed trend line, obtained using a locally weighted regression (LOESS),indicates a weak overall relationship, with minimal variation in pupil dilation across gaze durations. In the E-C direction, pupil dilation remains largely stable, suggesting that longer fixations do not significantly impact the cognitive load. In contrast, the C-E direction shows a slight increase in pupil dilation for shorter fixations (~250 ms), followed by a decline for longer durations (~750+ ms). This may indicate higher cognitive effort during initial fixations, followed by adaptation over prolonged gazes. Most fixations are brief (~250 ms), with greater variability at longer durations, particularly in the C-E condition, suggesting increased cognitive demand in specific translation segments. These findings highlight the importance of modeling the interaction between gaze event duration and AU type, as cognitive load appears to vary by translation direction and fixation length. We now proceed to visualize gaze event duration. As an example, we illustrate through Figure 8 the cognitive processing throughout Participant 13's complete English-Chinese translation task. The horizontal axis represents a typing event, and the vertical axis represents duration of eye gaze for that event, also known as AU. TT (red) dominates throughout, indicating the translator's sustained cognitive efforts directed predominantly toward text production. Longer-duration fixations (higher bars) in TT segments suggest points of greater cognitive difficulty or decision-making complexity in target text produc  
Figure 7: The relationship between pupil dilation and gaze event duration. tion. Parallel processing (green bars) appears frequently, showing the translator often simultaneously comprehends the source text and produces the target text. Frequent occurrences of parallel processing indicate moments when the translator actively integrates the comprehension of the source text with simultaneous text production. This aligns clearly with prior studies suggesting that translation often involves parallel cognitive effort as in [PERSON] [12]. ST processing (blue bars) occurs more frequently, but with a shorter duration, suggesting that the translator reads whole sentences to completion before starting their translation task. This aligns with [PERSON] and [PERSON]'s [29] findings on parallel processing, where translators gather information from the ST while producing the TT. To interpret and make sense of what is going on during the translation, we display the first 75 events of for Participant 13 in Figure 9. Early in the translation task (AU 1-20), Participant 13 mainly engaged with ST comprehension (blue bars). This clearly indicates an initial orientation phase, dedicated primarily to un-derstanding source content before typing. After initial comprehension, TT (red) and Parallel (green) processing clearly dominate, demonstrating frequent simultaneous comprehension-production activities. Clear instances of parallel processing highlight ongoing engagement with the source text even during active typing activities, reflecting cognitive multitasking during translation.