Learning perceptual skills is characterized by rapid improvements in performance within the first hour of training (fast perceptual learning) followed by more gradual improvements that take place over several daily practice sessions (slow perceptual learning). Although it is widely accepted that slow perceptual learning is accompanied by enhanced stimulus representation in sensory cortices, there is considerable controversy about the neural substrates underlying early and rapid improvements in learning perceptual skills. Here we measured event-related brain potentials while listeners were presented with 2 phonetically different vowels. Listeners' ability to identify both vowels improved gradually during the first hour of testing and was paralleled by enhancements in an early evoked response ( approximately 130 ms) localized in the right auditory cortex and a late evoked response ( approximately 340 ms) localized in the right anterior superior temporal gyrus and/or inferior prefrontal cortex. These neuroplastic changes depended on listeners' attention and were preserved only if practice was continued; familiarity with the task structure (procedural learning) was not sufficient. We propose that the early increases in cortical responsiveness reflect goal-directed changes in the tuning properties of auditory neurons involved in parsing concurrent speech signals. Importantly, the neuroplastic changes occurred rapidly, demonstrating the flexibility of human speech segregation mechanisms.

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Dot probe studies indicate that masked fearful faces modulate spatial attention. However, without a baseline to compare congruent and incongruent reaction times, it is unclear which aspect(s) of attention (orienting or disengagement) is affected. Additionally, backward masking studies commonly use a neutral face as the mask stimulus. This method results in greater perceptual inconsistencies for fearful as opposed to neutral faces. Therefore, it is currently unclear whether the effects of backward masked fearful faces are due to the fearful nature of the face or perceptual inconsistencies. Equally unclear, is whether this spatial attention effect is due to orienting or disengagement. Two modified dot probe experiments with neutral (closed mouth in Experiment 1) and smiling (open mouth in Experiment 2) masks were used to determine the role of perceptual inconsistencies in mediating the spatial attention effects elicited by masked fearful faces. The results indicate that masked fearful faces modulate the orienting of spatial attention, and it appears that this effect is due to the fearful nature of the face rather than perceptual inconsistencies between the initial faces and masks.