Category-Biased Neural Representations Form Spontaneously during Learning That Emphasizes Memory for Specific Instances.

Category learning, learning to sort a set of stimuli into categories or groups, can induce category biases in perception such that items in the same category are perceived as more similar than items from different categories. To what degree category bias develops when learning goals emphasize individuation of each stimulus and whether the bias emerges spontaneously during learning itself rather than in response to task demands is unclear. Here, we used functional MRI (fMRI) during encoding to test for category biases in neural representations of individual stimuli during learning. Human participants (males and females) encountered face-blend stimuli with unique first names and shared family names that indicated category membership. Participants were instructed to learn the full name for each face. Neural pattern classification and pattern similarity analyses were used to track category information in the brain. Results showed that stimulus category could be decoded during encoding across many frontal, parietal, and occipital regions. Furthermore, two stimuli from the same category were represented more similarly in the prefrontal cortex than two stimuli from different categories equated for physical similarity. These findings illustrate that a mere presence of category label can bias neural representations spontaneously during encoding to emphasize category-relevant information, even in the absence of explicit categorization demands and when category-irrelevant information remains relevant for task goals.SIGNIFICANCE STATEMENT Entities belonging to the same category are perceived as being more similar than entities belonging to different categories. Here, we show that neural representations highlighting category-relevant information form spontaneously during encoding. Notably, the presence of a category label led to neural category bias although participants focused on remembering individual stimuli and category-irrelevant stimulus features remained important for explicit task goals. These results may inform our understanding of bias in general and suggest that bias may emerge when category information is present even when one's explicit focus is on individuals.

Age effects on category learning, categorical perception, and generalization.

Age deficits in memory for individual episodes are well established. Less is known about how age affects another key memory function: the ability to form new conceptual knowledge. Here we studied age differences in concept formation in a category-learning paradigm with face-blend stimuli, using several metrics: direct learning of category members presented during training, generalisation of category labels to new examples, and shifts in perceived similarity between category members that often follow category learning. We found that older adults were impaired in direct learning of training examples, but that there was no significant age deficit in generalisation once we accounted for the deficit in direct learning. We also found that category learning affected the perceived similarity between members of the same versus opposing categories, and age did not significantly moderate this effect. Lastly, we compared traditional category learning to categorisation after a learning task in which a category label (shared last name) was presented alongside stimulus-specific information (unique first names that individuated category members). We found that simultaneously learning stimulus-specific and category information resulted in decreased category learning, and that this decrement was apparent in both age groups.

Perceived similarity ratings predict generalization success after traditional category learning and a new paired-associate learning task.

The current study investigated category learning across two experiments using face-blend stimuli that formed face families controlled for within- and between-category similarity. Experiment 1 was a traditional feedback-based category-learning task, with three family names serving as category labels. In Experiment 2, the shared family name was encountered in the context of a face-full name paired-associate learning task, with a unique first name for each face. A subsequent test that required participants to categorize new faces from each family showed successful generalization in both experiments. Furthermore, perceived similarity ratings for pairs of faces were collected before and after learning, prior to generalization test. In Experiment 1, similarity ratings increased for faces within a family and decreased for faces that were physically similar but belonged to different families. In Experiment 2, overall similarity ratings decreased after learning, driven primarily by decreases for physically similar faces from different families. The post-learning category bias in similarity ratings was predictive of subsequent generalization success in both experiments. The results indicate that individuals formed generalizable category knowledge prior to an explicit demand to generalize and did so both when attention was directed towards category-relevant features (Experiment 1) and when attention was directed towards individuating faces within a family (Experiment 2). The results tie together research on category learning and categorical perception and extend them beyond a traditional category-learning task.

Association of Age at Onset and Longitudinal Course of Prefrontal Function in Youth With Schizophrenia.

Importance: The extent of cognitive deterioration after schizophrenia (SZ) onset is poorly understood because prior longitudinal studies used small samples of older individuals with established illness. Objective: To examine the association of age at onset and subsequent longitudinal course of prefrontal activity during the first 2 years of illness in youths with SZ and healthy control participants (HCs). Design, Setting, and Participants: This naturalistic, longitudinal, functional magnetic resonance imaging (fMRI) study included patients with recent-onset SZ and HCs aged 12 to 25 years enrolled in an ongoing study of cognition in recent-onset psychosis in the Sacramento, California, area from October 13, 2004, through June 25, 2013. Participants completed clinical assessments and an established measure of cognitive control, the AX Continuous Performance Task (AX-CPT), during fMRI at baseline and at 6-, 12-, and 24-month follow-up. Whole-brain, voxelwise, and an a priori dorsolateral prefrontal cortex (DLPFC) region of interest analyses were performed. Group differences in developmental trajectories were examined by focusing on behavioral performance (d'-context) and cognitive control-associated brain activity. The association of antipsychotic medication and clinical factors were also examined. Data were analyzed from April 15, 2015, through August 29, 2017. Main Outcomes and Measures: Primary outcomes included group differences (HC vs SZ) in behavioral performance (d'-context from AX-CPT) and brain activity for cue B-A trials of the AX-CPT in an a priori DLPFC region of interest at baseline and across the age span. Secondary analysis examined the influence of antipsychotics on behavioral performance and DLPFC activity. Results: Among the sample of 180 participants (66.1% male; mean [SD] age at baseline, 19.2 [3.2] years), 87 patients with SZ (mean [SD] age, 19.6 [3.0] years) showed impaired performance compared with 93 HCs (mean [SD] age, 18.8 [3.4] years) across the age span (estimated difference [SE], -0.571 [0.12], d'-context; P < .001). Patients with SZ showed reduced activation in the DLPFC and parietal cortex (false discovery rate cluster corrected to P < .05) compared with HCs under conditions of high cognitive control at baseline. Region-of-interest analysis showed reduced activation in the DLPFC bilaterally for patients with SZ, with a trajectory that paralleled that of HCs across the age span (left DLPFC ß [SE] estimates, 0.409 [0.165] for the HC group and -0.285 [0.130] for the SZ group [main effect of group, P = .03]; right DLPFC ß [SE] estimates, 0.350 [0.103] for the HC group and -0.469 [0.157] for the SZ group [P = .003]). Antipsychotic medication, clinical symptoms, and global functioning were associated with SZ performance. Conclusions and Relevance: During the initial 1 to 2 years after illness onset, young individuals with SZ showed deficits in DLPFC activation and cognitive control, with developmental trajectories comparable to those of HCs. Younger age at onset was not associated with reduced cognition or activation. For individuals contributing to longitudinal analysis, results suggest that young patients do not show deterioration or disruption of ongoing brain development in the initial years after illness onset.

Remembering and imagining differentially engage the hippocampus: a multivariate fMRI investigation.

It has been proposed that imagining the future depends on the ability to retrieve episodic details from past experiences in order to recombine them into novel possible experiences; consequently, the processes of remembering and imagining rely on similar neural substrates, including the hippocampus. We used fMRI and both univariate and multivariate analysis techniques to test this prediction. Unbiased univariate analysis did not reveal differences in the hippocampus between remembering and imagining; however, multivariate analyses revealed evidence that patterns of activity within the hippocampus distinguish between remembering and imagining. Thus, while the hippocampus seems to be involved in both remembering the past and imagining the future, the pattern of activity within the hippocampus distinguishes between these two different tasks.