Abstract
Previous studies, mainly using a first-person perspective (1PP), have shown that the judgments of the hand laterality judgment (HLJ) task are dependent on biomechanical constraints (BC). Specifically, differing reaction times (RT) for hand pictures rotated medially or laterally around the mid sagittal plane are attributed to the BC effect on motor imagery. In contrast, we investigated whether the HLJ task is also subject to BC when performed from a third-person perspective (3PP) as well as 1PP using near-infrared spectroscopy (NIRS) to measure the brain activity of prefrontal cortex (PFC) in right-handed participants assigned to 1PP or 3PP groups. The 1PP group judged whether a presented hand was their own left or right hand, and the 3PP group whether it was the other’s left or right hand. Using their HLJ task error rates, the 1PP and 3PP groups were subdivided into an Error Group (EG) and No Error Group (NEG). For the 1PP group, both EG and NEG showed a significant Hand Laterality × Orientation interaction for RT, indicating the BC effect on motor imagery. For the 3PP group, however, neither EG nor NEG showed the interaction, even though EG showed a significantly longer RT than NEG. These results suggest that the 3PP EG appropriately followed the 3PP task instruction, while the NEG might have taken 1PP. However, the 3PP EG NIRS profile of left PFC showed a significant Hand Laterality × Orientation interaction, while the 1PP EG did not. More noteworthy is that the left PFC activation of EG showed an interaction between the 1PP and 3PP groups when the left hand was presented. Furthermore, in the NEG, the PFC activation was not influenced by the BC in either the 1PP or 3PP condition. These results indicate that BC interferes with the HLJ task performed from the 1PP and 3PP.
Highlights
Shepard and Metzler [1] demonstrated that mental rotation (MR) is the cognitive process of imaging an object rotating from one orientation to another
We subdivided the participants in both the 1PP and 3PP groups into No Error Group (NEG) and Error Group (EG) according to their error rates in the hand laterality judgment (HLJ) task, which accounted for 0% response in the NEG and for 3.93% in the EG
In the 3PP condition, the results revealed that the main effect of Performance level was significant (F(1,35) = 5.15, p < .05, η2 = 0.13) due to the fact that the mean reaction time (RT) was significantly longer for the EG (1972.89 ms) than that for the NEG (1317.63 ms), and the main effect of Orientation was significant (F(1,35) = 4.76, p < .05, η2 = 0.12)
Summary
Shepard and Metzler [1] demonstrated that mental rotation (MR) is the cognitive process of imaging an object rotating from one orientation to another They reported that the reaction time (RT) required to judge whether the pairs of two three-dimensional cubes were the same increased linearly with greater angular disparity between the two cubes. Several studies found that “The time required for the laterality (left or right) of a hand presented in different views and angular orientations is similar to the time taken to execute a corresponding movement” [6,7,8,9,10] These results suggest that the “Hand stimuli are automatically coded with respect to an egocentric (internal) perspective (i.e., according to the viewpoint consistent with looking at one’s own body)” [11]. These results of BC effect were interpreted as indicating that motor imagery plays a critical role in the HLJ task, while visual imagery plays a dominant role in the MR of an object task [12]
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