The most commonly accepted theory on how the cognitive system creates a mental representation of a visual stimulus is that representations emerge through a step-by-step process, in which subjects visually perceive individual segments of a stimulus and internalize the pieces to represent the whole stimulus, also known as the piecemeal strategy. Subjects commonly rotated one object clock-wise or counter clock-wise until it visually matches or mismatches the target object, and then make the decision 2. Shepard and Metzler displayed projections of two unfamiliar three-dimensional (3D) figures and instructed subjects to determine whether the two figures were identical or not despite the differences in orientation 1. How we determine that figure objects have the same shape despite differences in orientation or size is a common problem in the study of visual perception. Spatial abilities are important cognitive skills that are used in various everyday tasks, such as learning the environment, and during academic activities. Our study did confirm that there are differences in processing states between these two of mental-rotation strategies, and were consistent with the previous suggestion that mental rotation is discrete process that is accomplished in a piecemeal fashion. Additionally, we applied three classification methods, logistic regression, support vector model and dHMM, of which dHMM predicted the strategies with the highest accuracy (76.8%). Eye movements were found to contain the necessary information for determining the processing strategy, and the dHMM that best fit our data segmented the mental-rotation process into three hidden states, which we termed encoding and searching, comparison, and searching on one-side pair. Inference was carried out using an advanced statistical modelling and data-driven approach – a discriminative hidden Markov model (dHMM) trained using eye-movement data obtained from an experiment consisting of two different strategies: (I) mentally rotate the right-side figure to be aligned with the left-side figure and (II) mentally rotate the left-side figure to be aligned with the right-side figure. Here, we investigated how processing states alternate during mental-rotation tasks. Mental-rotation tasks are assumed to involve five or three sequential cognitive-processing states, though this has not been demonstrated experimentally. Mental rotation is an important paradigm for spatial ability.
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