THE INFLUENCE OF CONCEPTUAL KNOWLEDGE ON VISUAL DISCRIMINATION

Comparison and the development of knowledge

This paper considers the role of comparison in the development of knowledge. Results show that comparing similar objects makes them appear more similar. Comparing dissimilar objects, on the other hand does not make them appear more similar, and in some circumstances may make them appear less similar. The effect of comparison on similar items was especially striking since participants judged items to be more similar after comparison even if the comparison task was to list differences between the two items. Further, this effect appears specific to comparison and does not appear to be simply due to a "fleshing out" of object representations (listing properties of two objects without comparing the objects themselves served to increase the objects' similarity regardless of whether the objects were similar or dissimilar to start). This suggests that comparison may play a special role in partitioning bits of experience into categories, sharpening categorical boundaries, and otherwise helping us create conceptual structure above and beyond that offered by the world.

The influence of visual and nonvisual attributes in visual object identification

To elucidate the role of visual and nonvisual attribute knowledge on visual object identification, we present data from three patients, each with visual object identification impairments as a result of different etiologies. Patients were shown novel computer-generated shapes paired with different labels referencing known entities. On test trials they were shown the novel shapes alone and had to identify them by generating the label with which they were formerly paired. In all conditions the same triad of computer-generated shapes were used. In one condition, the labels (banjo, guitar, violin) referenced entities that were both visually similar and similar in terms of their nonvisual attributes within semantics. In separate conditions we used labels (e.g., spike, straw, pencil or snorkel, cane, crowbar) that referenced entities that were similar in terms of their visual attributes but were dissimilar in terms of their nonvisual attributes. The results revealed that nonvisual attribute information profoundly influenced visual object identification. Our patients performed significantly better when attempting to identify shape triads whose labels referenced objects with distinct nonvisual attributes versus shape triads whose labels referenced objects with similar nonvisual attributes. We conclude that the nonvisual aspects of meaning must be taken into consideration when assessing visual object identification impairments.

Visual expertise with nonface objects leads to competition with the early perceptual processing of faces in the human occipitotemporal cortex

Human electrophysiological studies have found that the processing of faces and other objects differs reliably at approximately 150 ms after stimulus onset, faces giving rise to a larger occipitotemporal field potential on the scalp, termed the N170. We hypothesize that visual expertise with nonface objects leads to the recruitment of early face-related categorization processes in the occipitotemporal cortex, as reflected by the N170. To test this hypothesis, the N170 in response to laterally presented faces was measured while subjects concurrently viewed centrally presented, novel, nonface objects (asymmetric "Greebles"). The task was simply to report the side of the screen on which each face was presented. Five subjects were tested during three event-related potential sessions interspersed throughout a training protocol during which they became experts with Greebles. After expertise training, the N170 in response to faces was substantially decreased ( approximately 20% decrease in signal relative to that when subjects were novices) when concurrently processing a nonface object in the domain of expertise, but not when processing untrained objects of similar complexity. Thus, faces and nonface objects in a domain of expertise compete for early visual categorization processes in the occipitotemporal cortex.

Conceptual and perceptual information both influence melody identification

Three processes have been identified as central to object identification: top-down processing, bottom-up processing, and lateral competition. Six experiments using the perceptual interference paradigm were conducted to assess the relative contributions of these three processes to melody identification. Significant interference was observed only when the target and the distracting information were difficult to distinguish both perceptually and conceptually. Lateral competition-the activation of specific distractor melodies--did not influence the magnitude of interference observed. These results suggest that bottom-up and top-down processes contribute more to melody identification than does lateral competition. The data are discussed in terms of the broader literature on object identification and the relationship between identifying melodies, spoken words, and visual objects.

Auditory and action semantic features activate sensory-specific perceptual brain regions

Traditionally, concepts were considered propositional, amodal, and verbal in nature (for review, see ). Recent findings, however, suggest that conceptual knowledge is divisible into different types (L. Wu and L.W. Barsalou, personal communication, ) and that each type may be linked to specific sensory and motor processes. This implies that sensory processing regions of the brain may also process concepts. In fact, there is some neuroimaging evidence that conceptual information does activate perceptual brain regions and that there is a correspondence between knowledge type and the region being activated. In the following experiment, using a training technique developed in previous studies, participants verbally learned associations between novel objects and conceptual features. The objective was to create objects that were associated with features from only one knowledge type, something that does not occur with common objects. During a visual task that did not require retrieval of learned associations, the superior temporal gyrus, which responds well to sounds, was preferentially activated by objects associated with auditory features (e.g., buzzes). Likewise, the posterior superior temporal sulcus, which responds well to motion, was preferentially activated by objects associated with "action" features (e.g., hops). These findings support the theory that knowledge is grounded in perception.

Laterality effects in the recognition of depth-rotated novel objects

The dissociable neural subsystems theory proposes that left-hemisphere (LH) performance is dominated by a viewpoint-invariant (VI) recognition subsystem, whereas right-hemisphere (RH) performance is dominated by a viewpoint-dependent (VD) subsystem (Marsolek, 1999). Studies supporting this theory have used familiar objects and, therefore, may have been confounded by characteristics beyond perceptual features. Experiment 1, a lateralized sequential-matching task with novel objects, showed VD recognition in both hemispheres. In Experiment 2, some participants learned semantic associations for four novel objects, whereas others were exposed to the novel objects without the semantic associations. Both groups later performed a depth-rotated lateralized sequential-matching task. The participants who had learned semantic associations showed greater VD performance in the RH than in the LH; however, the participants in the control group showed equivalent VD performance in both hemispheres. The results suggest that hemispheric differences in VD performance may be partially attributable to an LH advantage for semantic processing.

Brain areas engaged during visual judgments by involuntary access to novel semantic information

Theories of visual recognition place different emphasis on the role of non-stimulus factors. Previously, we showed that arbitrary semantic associations influenced visual recognition of novel objects. Here, the neural substrate of this effect was investigated. During a visual task, novel objects associated with arbitrary semantic features produced more activation in frontal and parietal cortex than objects associated with names. Because the task required no semantic retrieval, access to semantics appears to be involuntary. The brain regions involved have been implicated in semantic processing, thus recently acquired semantics activate a similar network to semantics learned over a lifetime.