Perceptual deterioration is reflected in the neural response: fMRI study of nappers and non-nappers

Repeated training on a perceptual task can result in performance deterioration. In the case of vision, this practice-dependent decrease, or perceptual deterioration is restored by changing the target orientation, spatial location, or by taking a daytime nap. Behavioral studies suggest the locus of these performance changes to be primary visual cortex. We used fMRI to directly probe whether perceptual deterioration and nap-dependent maintenance of performance can be detected at the level of primary visual cortex. We also asked whether these changes are due to a bottom-up, stimulus-driven response or a top-down plasticity of attentional mechanisms. Subjects were scanned while performing a texture-discrimination task. Half the subjects took a nap between sessions. We measured the relationship between changes in performance and changes in BOLD signal modulation between the two groups. Non-nappers showed performance deterioration that was significantly correlated with decreased BOLD signal modulation, exclusively in area V1 and limited to the bottom-up condition. In contrast, no change was detected in performance and BOLD response in the two conditions for nappers. These results indicate that napping prevented performance deterioration, which was reflected in the fMRI response of neurons in V1. Without a nap, perceptual deterioration was related to decreases in the stimulus-driven, bottom-up representation, rather than decreases in attentional modulation to the stimulus.     

Word frequency effects in high-dimensional co-occurrence models: A new approach

The HAL (hyperspace analog to language) model of lexical semantics uses global word co-occurrence from a large corpus of text to calculate the distance between words in co-occurrence space. We have implemented a system called HiDEx (High Dimensional Explorer) that extends HAL in two ways: It removes unwanted influence of orthographic frequency from the measures of distance, and it finds the number of words within a certain distance of the word of interest (NCount, the number of neighbors). These two changes to the HAL model produce     

When Reparation Is Impossible: A Discussion of “‘When Reparation Is Felt to Be Impossible’: Persecutory Guilt and Breakdowns in Thinking and Dialogue about Race”

In this paper, Dr. Kali Cyrus thoughtfully responds to Dr. Jane Caflisch’s comments (this issue) on the schizoid-inducing nature of racial conflict for white people. Using personal and professional experiences confronting racially complex dilemmas, Dr. Cyrus describes why ultimately, repair of racial trauma may be impossible for white people to achieve but is nevertheless worth the pursuit.