Biomedical subjects

Thomas W James

Publications and source records attributed to Thomas W James.

10 recordsLinked to original sources

PubMed2006

Repetition-induced changes in BOLD response reflect accumulation of neural activity.

Recent exposure to a stimulus improves performance with subsequent identification of that same stimulus. This ubiquitous, yet simple, memory phenomenon is termed priming and has been linked to another widespread phenomenon called repetition suppression, which is a repetition-induced reduction in human brain activation as measured using fMRI. Here, competing models of the neural basis of repetition suppression were tested empirically. In a backward masking paradigm, we found that effectively masked object stimuli showed repetition enhancement of brain activation instead of suppression. This finding is consistent with an Accumulation model, but is inconsistent with a Suppression model of neural activity. Enhanced activation and the improved behavioral performance usually associated with priming are both explained by a shift in peak latency of the population neural activity elicited during identification.

Brain↗

PubMed2005

Haptic face identification activates ventral occipital and temporal areas: an fMRI study.

Many studies in visual face recognition have supported a special role for the right fusiform gyrus. Despite the fact that faces can also be recognized haptically, little is known about the neural correlates of haptic face recognition. In the current fMRI study, neurologically intact participants were intensively trained to identify specific facemasks (molded from live faces) and specific control objects. When these stimuli were presented in the scanner, facemasks activated left fusiform and right hippocampal/parahippocampal areas (and other regions) more than control objects, whereas the latter produced no activity greater than the facemasks. We conclude that these ventral occipital and temporal areas may play an important role in the haptic identification of faces at the subordinate level. We further speculate that left fusiform gyrus may be recruited more for facemasks than for control objects because of the increased need for sequential processing by the haptic system.

Adult↗

PubMed2005

Generating complex three-dimensional stimuli (Greebles) for haptic expertise training.

An apparatus is described that accurately measures response times and video records hand movements during haptic object recognition using complex three-dimensional (3-D) forms. The apparatus was used for training participants to become expert at perceptual judgments of 3-D objects (Greebles) using only their sense of touch. Inspiration came from previous visual experiments, and therefore training and testing protocols that were similar to the earlier visual procedures were used. Two sets of Greebles were created. One set (clay Greebles) was hand crafted from clay, and the other (plastic Greebles) was machine created using rapid prototyping technology. Differences between these object creation techniques and their impact on perceptual expertise training are discussed. The full set of these stimuli may be downloaded from www.psychonomic.org/archive/.

Humans↗

PubMed2004

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.

Adult↗

PubMed2004

Neural synergy between kinetic vision and touch.

Ambiguous visual information often produces unstable visual perception. In four psychophysical experiments, we found that unambiguous tactile information about the direction of rotation of a globe whose three-dimensional structure is ambiguous significantly influences visual perception of the globe. This disambiguation of vision by touch occurs only when the two modalities are stimulated concurrently, however. Using functional magnetic resonance imaging, we discovered that touching the rotating globe, even when not looking at it, reliably activates the middle temporal visual area (MT+), a brain region commonly thought to be crucially involved in registering structure from motion. Considered together, our results show that the brain draws on somatosensory information to resolve visual conflict.

Brain↗

PubMed2004

Perceiving object motion using vision and touch.

In a previous experiment, we showed that bistable visual object motion was partially disambiguated by tactile input. Here, we investigated this effect further by employing a more potent visuotactile stimulus. Monocular viewing of a tangible wire-frame sphere (TS) rotating about its vertical axis produced bistable alternations of direction. Touching the TS biased simultaneous and subsequent visual perception of motion. Both of these biases were in the direction of the tactile stimulation and, therefore, constituted facilitation or priming, as opposed to interference or adaptation. Although touching the TS biased visual perception, tactile stimulation was not able to override the ambiguous visual percept. This led to periods of sensory conflict, during which visual and tactile motion percepts were incongruent. Visual and tactile inputs can sometimes be fused to form a coherent percept of object motion but, when they are in extreme conflict, can also remain independent.

Cues↗

PubMed2003

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.

Acoustic Stimulation↗

PubMed2003

Ventral occipital lesions impair object recognition but not object-directed grasping: an fMRI study.

D.F., a patient with severe visual form agnosia, has been the subject of extensive research during the past decade. The fact that she could process visual input accurately for the purposes of guiding action despite being unable to perform visual discriminations on the same visual input inspired a novel interpretation of the functions of the two main cortical visual pathways or 'streams'. Within this theoretical context, the authors proposed that D.F. had suffered severe bilateral damage to her occipitotemporal visual system (the 'ventral stream'), while retaining the use of her occipitoparietal visual system (the 'dorsal stream'). The present paper reports a direct test of this idea, which was initially derived from purely behavioural data, before the advent of modern functional neuroimaging. We used functional MRI to examine activation in her ventral and dorsal streams during object recognition and object-directed grasping tasks. We found that D.F. showed no difference in activation when presented with line drawings of common objects compared with scrambled line drawings in the lateral occipital cortex (LO) of the ventral stream, an area that responded differentially to these stimuli in healthy individuals. Moreover, high-resolution anatomical MRI showed that her lesion corresponded bilaterally with the location of LO in healthy participants. The lack of activation with line drawings in D.F. mirrors her poor performance in identifying the objects depicted in the drawings. With coloured and greyscale pictures, stimuli that she can identify more often, D.F. did show some ventral-stream activation. These activations were, however, more widely distributed than those seen in control participants and did not include LO. In contrast to the absent or abnormal activation observed during these perceptual tasks, D.F. showed robust activation in the expected dorsal stream regions during object grasping, despite considerable atrophy in some regions of the parietal lobes. In particular, an area in the anterior intraparietal sulcus was activated more for grasping an object than for just reaching to that object, for both D.F. and controls. In conclusion, we have been able to confirm directly that D.F.'s visual form agnosia is associated with extensive damage to the ventral stream, and that her spared visuomotor skills are associated with visual processing in the dorsal stream.

Agnosia↗

PubMed2002

Differential effects of viewpoint on object-driven activation in dorsal and ventral streams.

Using fMRI, we showed that an area in the ventral temporo-occipital cortex (area vTO), which is part of the human homolog of the ventral stream of visual processing, exhibited priming for both identical and depth-rotated images of objects. This pattern of activation in area vTO corresponded to performance in a behavioral matching task. An area in the caudal part of the intraparietal sulcus (area cIPS) also showed priming, but only with identical images of objects. This dorsal-stream area treated rotated images as new objects. The difference in the pattern of priming-related activation in the two areas may reflect the respective roles of the ventral and dorsal streams in object recognition and object-directed action.

Adult↗

PubMed2002

Haptic study of three-dimensional objects activates extrastriate visual areas.

In humans and many other primates, the visual system plays the major role in object recognition. But objects can also be recognized through haptic exploration, which uses our sense of touch. Nonetheless, it has been argued that the haptic system makes use of 'visual' processing to construct a representation of the object. To investigate possible interactions between the visual and haptic systems, we used functional magnetic resonance imaging to measure the effects of cross-modal haptic-to-visual priming on brain activation. Subjects studied three-dimensional novel clay objects either visually or haptically before entering the scanner. During scanning, subjects viewed visually primed, haptically primed, and non-primed objects. They also haptically explored non-primed objects. Visual and haptic exploration of non-primed objects produced significant activation in several brain regions, and produced overlapping activation in the middle occipital area (MO). Viewing visually and haptically primed objects produced more activation than viewing non-primed objects in both area MO and the lateral occipital area (LO). In summary, haptic exploration of novel three-dimensional objects produced activation, not only in somatosensory cortex, but also in areas of the occipital cortex associated with visual processing. Furthermore, previous haptic experience with these objects enhanced activation in visual areas when these same objects were subsequently viewed. Taken together, these results suggest that the object-representation systems of the ventral visual pathway are exploited for haptic object perception.

Adult↗