Confidence-accuracy relations for faces and scenes: roles of features and familiarity.

Using naturalistic scenes, we recently demonstrated that confidence-accuracy relations differ depending on whether recognition responses are based on memory for a specific feature or instead on general familiarity: When confidence is controlled for, accuracy is higher for familiarity-based than for feature-based responses. In the present experiment, we show that these results generalize to face recognition. Subjects studied photographs of scenes and faces presented for varying brief durations and received a recognition test on which they (1) indicated whether each picture was old or new, (2) rated their confidence in their response, and (3) indicated whether their response was based on memory for a feature or on general familiarity. For both stimulus types, subjects were more accurate and more confident for their feature-based than for their familiarity-based responses. However, when confidence was held constant, accuracy was higher for familiarity-based than for feature-based responses. These results demonstrate an important similarity between face and scene recognition and show that for both types of stimuli, confidence and accuracy are based on different information.

Different confidence-accuracy relationships for feature-based and familiarity-based memories.

Participants studied naturalistic pictures presented for varying brief durations and then received a recognition test on which they indicated whether each picture was old or new and rated their confidence. In 1 experiment they indicated whether each "old"/"new" response was based on memory for a specific feature in the picture or instead on the picture's general familiarity; in another experiment, we defined pictures that tended to elicit feature versus familiarity responses. Thus, feature/familiarity was a dependent variable in 1 experiment and an independent variable in the other. In both experiments feature-based responses were more accurate than those that were familiarity based, and confidence and accuracy increased with duration for both response types. However, when confidence was controlled for, mean accuracy was higher for familiarity-based than for feature-based responses. The theoretical implication is that confidence and accuracy arise from different underlying information. The applied implication is that confidence differences should not be taken as implying accuracy differences when the phenomenal basis of the memory reports differ.

A significant bilateral field advantage for shapes defined by static and motion cues.

Matching performance is better when pairs of visual stimuli are presented in bilateral conditions--in which one stimulus is presented to each side of the visual field--than in unilateral presentations-when both stimuli are presented to one side of the field. This is called the bilateral field advantage (BFA). The processing of visual motion has also been found to be more strongly integrated across the cerebral hemispheres than is processing of static cues. However, in these studies higher-order motion tasks, such as processing motion-defined form, have not been examined. To determine if the BFA generalises to such tasks, we measured the magnitude of the effect using a shape-matching task in which the stimuli were random polygons that were either in motion, motion-defined, or static. The polygon pairs were presented either: (i) bilaterally, one to either side of the vertical meridian; (ii) unilaterally, both to one side of the vertical meridian (left or right visual fields); or (iii) centrally, vertically separated across the horizontal meridian (a control condition). An equal advantage of bilateral conditions over unilateral ones was found for all three types of polygon shape cues, showing that the BFA generalises to conditions where shapes are in motion and where shape is defined by motion. These findings are compatible with the notion that motion processing is strongly integrated across the cerebral hemispheres, and with the idea that this integration manifests itself with simple motion information, rather than with higher-order motion processing such as matching shapes defined by motion.

Proinflammatory cytokines differentially influence adult hippocampal cell proliferation depending upon the route and chronicity of administration.

Disturbances of hippocampal plasticity, including impaired dendritic branching and reductions of neurogenesis, are provoked by stressful insults and may occur in depression. Although corticoids likely contribute to stressor-induced reductions of neurogenesis, other signaling messengers, including pro-inflammatory cytokines might also be involved. Accordingly, the present investigation assessed whether three proinflammatory cytokines, namely interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha) (associated with depression) influenced cellular proliferation within the hippocampus. In this regard, systemic administration of TNF-alpha reduced 5-bromo-2-deoxyuridine (BrdU) labeling within the hippocampus, whereas IL-1beta and IL-6 had no such effect. However, repeated but not a single intra-hippocampal infusion of IL-6 and IL-1beta actually increased cellular proliferation and IL-6 infusion also enhanced microglial staining within the hippocampus. Yet, no changes in doublecortin expression were apparent, suggesting that the cytokine did not influence the birth of cells destined to become neurons. Essentially, the route of administration and chronicity of cytokine administration had a marked influence upon the nature of hippocampal alterations provoked, suggesting that cytokines may differentially regulate hippocampal plasticity in neuropsychiatric conditions.