Metacognition and metacognitive monitoring in aging.

Relating what we see to what we know is an essential cognitive function for humans, enabling us to draw on prior experience to successfully detect, recognize, and interact with objects in the world. Doing so requires rapid and reliable evaluation of the similarity between incoming sensory information and stored representations (; ; ; ). Despite its ubiquity, this process of comparison is inherently complex, as objects themselves are defined by a myriad of both observable visual properties (e.g., color, surface, texture, global shape) and more abstract, conceptual attributes (e.g., biological status, action affordances, abstract qualities) (; ; ; ; ). As such, objects can be both similar different from one another, depending on the dimension under consideration. For example, an alligator and a rabbit are at once both vastly disparate—one is large, scaly, and dangerous; the other small, fluffy, and cute—and yet fundamentally similar, as both are animals that breathe, eat, and reproduce. Recent large-scale efforts to characterize the multidimensional nature of object representations have uncovered a host of dimensions that underlie human judgments of similarity both across (; ; ) and within () overarching object categories. Findings suggest that both perceptual and conceptual attributes serve to structure object representations in the human visual system. Identified perceptual dimensions capture intrinsic properties of the visual appearance of objects (e.g., roundness, elongation, color, flatness, shininess, texture), where conceptual dimensions encompass both taxonomic category (e.g., animal, vehicle, plant) and higher-level, semantically rich aspects of object meaning (e.g., associations of value, heat, disgust). Disentangling how perceptual and conceptual object properties emerge in time-resolved magnetoencephalography (MEG) and electroencephalography (EEG) neural responses has been a focus within existing work on the temporal unfolding of visual object processing (; ; ; ; ; ; ; ). This is important, because perceptual and conceptual object attributes often covary: Think of a and a , which are similar in terms of not only material composition, size, and shape but also function, affordance, and taxonomic status (graspable tools). As a collective, these studies suggest that perceptual features give rise to early, stimulus-locked activity patterns—reflecting rapid encoding of the visual features of objects—where representations of conceptual properties tend to emerge comparatively later in the neural time course, suggesting a temporal cascade from early perceptual analysis to later semantic integration (; ; ; ; ; ). Notably, neural representations of conceptual features also show greater variability across individuals, potentially reflecting differences in experience, familiarity, or conceptual organization (). In addition to perceptual and conceptual features, object knowledge also comprises contextual attributes, defined by the predictable associations of objects with certain environments (e.g., a toothbrush in a bathroom, a knife on a countertop). A wealth of prior work has shown that contextual associations between objects and surrounding scenes influence how we search for and recognize objects (; ; ; ; ; ), with scene context even serving to disambiguate neural representations for degraded objects that are otherwise unrecognizable (; ). Context-based facilitation also arises at the inter-object level, with observers recognizing objects more efficiently when they are contextualized by a second, related object (; ; ; ; ; ; ). Moreover, violations of canonical contextual associations seem to elicit reliable neural signals even when observers are not explicitly attending to congruity between the elements (; ; ), suggesting that representations of contextual object attributes may be evoked automatically during object processing.