Of the previous studies that have investigated generalization of perceptual learning across tasks, most have reported a lack of transfer (Crist, Kapadia, Westheimer, & Gilbert,
1997; Fahle,
1997; Meinhardt,
2002; Petrov & Van Horn,
2012; Saffell & Matthews,
2003; Shiu & Pashler,
1992). While some of the tasks in question are likely to recruit distinct populations of neurons to perform the required judgments, and were therefore never likely to lead to transfer, it is less clear why some studies demonstrated specificity. Saffell and Matthews (
2003) showed that training on speed or direction discriminations task failed to transfer to one another, or to a luminance discrimination control task. As in the current study, the stimulus was the same for all tasks (random-dot kinematograms) and the experimental tasks can claim to have at least partially overlapping neural representations (e.g., Rodman & Albright,
1987). While there is evidence that a subpopulation of neurons in visual area MT demonstrate selectivity for velocity (i.e., neurons tuned for both speed and direction, Rodman & Albright,
1987), speed and direction discrimination tasks can be performed independent of each other. For instance, our ability to perform a speed discrimination task does not depend on the direction of motion (Matthews & Qian,
1999), while the speed of the stimulus has a relatively small influence on performance in a direction discrimination task (De Bruyn & Orban,
1988). This is not the case for our tasks; a precursor to performing the curvature task is to resolve the orientation of the Gabor elements. Similarly, the orientation and curvature of the Gabor elements must be resolved to complete the global form task. Interestingly, in one of the few studies to demonstrate transfer between different tasks, Huang, Lu, Tjan, Zhou, and Liu (
2007) showed that training on a direction discrimination task transferred to a motion detection task, but not vice versa. The authors use a similar rationale to explain their results; whereas the discrimination task requires the detection of the coherent motion signal, the exact direction of motion is irrelevant when performing the detection task. Together these results suggest that the relationship between different tasks is an important factor to consider in designing perceptual learning paradigms.