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PubMed2006

Neural basis subserving the detection of postural instability: an fMRI study.

Human upright posture is a product of a complex dynamic system that relies on integration of input from multimodal sensory sources. Extensive research has explored the role of visual, vestibular, and somatosensory systems in the control of upright posture. However, the role of higher cognitive function in a participant's assessment of postural stability has been less studied. In previous research, we showed specific neural activation patterns in EEG associated with recognition of unstable postures in young healthy participants. Similar EEG patterns have been recently observed in regulation of posture equilibrium in dynamic stances. This article evaluates participants' postural stability in dynamic stances and neural activation patterns underlying visual recognition of unstable postures using event-related functional MRI (fMRI). Our results show that the "stable" participants were successful in recognition of unstable postures of a computer-animated body model and experienced egocentric motion. Successful recognition of unstable postures in these participants induces activation of distinct areas of the brain including bilateral parietal cortex, anterior cingulate cortex, and bilateral cerebellum. In addition, significant activation is observed in basal ganglia (caudate nucleus and putamen) but only during perception of animated postures. Our findings suggest the existence of modality-specific distributed activation of brain areas responsible for detection of postural instability.

Adult↗
PubMedDate not supplied

Electrophysiological studies of human face perception. III: Effects of top-down processing on face-specific potentials.

This is the last in a series of papers dealing with intracranial event-related potential (ERP) correlates of face perception. Here we describe the results of manipulations that may exert top-down influences on face recognition and face-specific ERPs, and the effects of cortical stimulation at face-specific sites. Ventral face-specific N200 was not evoked by affective stimuli; showed little or no habituation; was not affected by the familiarity or unfamiliarity of faces; showed no semantic priming; and was not affected by face-name learning or identification. P290 and N700 were affected by semantic priming and by face-name learning and identification. The early fraction of N700 and face-specific P350 exhibited significant habituation. About half of the AP350 sites exhibited semantic priming, whereas the VP350 and LP350 sites did not. Cortical stimulation evoked a transient inability to name familiar faces or evoked face-related hallucinations at two-thirds of face-specific N200 sites. These results are discussed in relation to human behavioral studies and monkey single-cell recordings. Discussion of results of all three papers concludes that: face-specific N200 reflects the operation of a module specialized for the perception of human faces; ventral and lateral occipitotemporal cortex are composed of a complex mosaic of functionally discrete patches of cortex of variable number, size and location; in ventral cortex there is a posterior-to-anterior trend in the location of patches in the order letter-strings, form, hands, objects, faces and face parts; P290 and N700 at face-specific N200 sites, and face-specific P350, are subject to top-down influences.

Arousal↗
PubMed1992

Rate coherence and event coherence in the visual cortex: a neuronal model of object recognition.

We propose a function-oriented model of the visual cortex. The model addresses an essential task of the visual system: to detect and represent objects. These are defined as sets, which reappear in the input with invariant inner relations. A network, incorporating an idealized description of anatomical and physiological data, is presented with a movie showing various moving objects. In the course of time, as a result of Hebbian plasticity, a connection scheme develops which embodies in its forward and lateral connections the information necessary to perform the operations involved in object recognition. We demonstrate that coherent neural activity can exploit this information. Two types of coherence have to be distinguished in this respect. Rate coherence performs invariance operations and association, while event coherence accomplishes segmentation tasks. The model reproduces and explains experimental findings made both in physiological recordings from the visual cortex and in psychophysical studies.

Animals↗
PubMed1994

A network model for generating differential symmetry axes of shapes via receptive fields.

Some symmetries (e.g. bilateral, rotational, translational) only describe quite specialized shapes, but differential symmetry axes (e.g. Blum, J. Theoret. Biol. 38, 205-287, 1973; Brady and Asada, Int. J. Robotics Res. 3, 36-61, 1984) describe more general shapes. Such axes are of interest in part because they form the 'backbone' of generalized cylinder and other shape representations used in shape recognition (e.g. Marr, Vision, W. H. Freeman and Co., NY, 1982; Biederman, Psychol. Rev. 94, 115-147, 1987). However, despite the popularity of these representations as psychological models, algorithms from machine vision for computing them have strong limitations as psychological models. This paper presents two versions of a network model, one of which is more plausible as a psychological model because it derives symmetry axes from the activations of idealized visual receptive fields.

Form Perception↗
PubMed2006

Basal forebrain amnesia: a case study.

OBJECTIVE: To provide new evidence of the existence of basal forebrain amnesia, as a different entity from hippocampal or diencephalic amnesia. BACKGROUND: Some authors consider that the characteristics of amnesia do not depend on lesion site, although others claim there are neuropsychologic differences between amnesias due to hippocampal, diencephalic, and basal forebrain lesions. As to the latter, literature is scarce and controversial. The opportunity to thoroughly study J.S., a man with a high IQ and amnesia, enabled us to reinforce the second hypothesis. METHODS: J.S. is a 47-year-old man who underwent surgery for a pituitary adenoma, the resulting lesion involving only the basal forebrain. We gave him a complete neuropsychologic battery for amnesia and executive functions. RESULTS: J.S. showed severe amnesia with a flat learning curve, a rapid forgetting rate and good recognition, a temporal gradient of several years for remote memory, preserved semantic and procedural memory. Most of the tests for executive functions were normal, although he did have a significant personality change after surgery. CONCLUSIONS: This patient is different from patients with hippocampal or diencephalic lesions, and is similar to other patients reported with basal forebrain lesions. The main difference is the relation between his flat learning curve and preserved recognition, both for visual and verbal material.

Adenoma↗
PubMed2003

Shared and dissociated cortical regions for object and letter processing.

The present study determined the extent to which object and letter recognition recruit similar or dissociated neural resources. Participants passively viewed and silently named line drawings of objects, single letters, and visual noise patterns and centrally fixated an asterisk. We used whole-brain functional MRI and a very conservative approach to hypothesis testing that distinguished among brain regions that were selectively activated by different experimental conditions and those that were conjointly activated. The left fusiform gyrus (BA 19 & 37) and left inferior frontal cortex BA(44/6) showed a greater degree of conjoined activation for objects and letters than selective activation for either category, whereas left inferior parietal cortex (BA 40) and the left insula showed a strong letter-selective response. Equal recruitment of left fusiform and inferior frontal regions by objects and letters reflects similar demands on cognitive processing by these two categories and argues against category-specific modules in these regions. However, cortical systems for object and letter processing are not completely shared given the exclusive activation of left inferior parietal cortex by letters.

Adult↗
PubMed2005

Neural correlates of consciousness: a definition of the dorsal and ventral streams and their relation to phenomenology.

The paper presents a hypothesis for a neural correlate of consciousness. A proposal is made that both the dorsal and ventral streams must be concurrently active to generate conscious awareness and that V1 (striate cortex) provides a serial link between them. An argument is presented against a true extrastriate communication between the dorsal and ventral streams. Secondly, a detailed theory is developed for the structure of the visual hierarchy. Premotor theory states that each organism-object interaction can be described by the two quantitative measures of torque and change in joint position served by the basal ganglia and cerebellum, respectively. This leads to a component theory of motor efference copy providing a fundamental tool for categorizing dorsal and ventral stream networks. The rationale for this is that the dorsal stream specifies spatial coordinates of the external world, which can be coded by the reafference of changes in joint position. The ventral stream is concerned with object recognition and is coded for by forces exerted on the world during a developmental exploratory phase of the organism. The proposed pathways for a component motor efference copy from both the cerebellum and basal ganglia converge on the thalamus and modulate thalamocortical projections via the thalamic reticular nucleus. The origin of the corticopontine projections, which are a massive pathway for cortical information to reach the cerebellum, coincides with the area typically considered as part of the dorsal stream, whereas the entire cortex projects to the striatum. This adds empirical support for a new conceptualization of the visual streams. The model also presents a solution to the binding problem of a neural correlate of consciousness, that is, how a distributed neural network synchronizes its activity during a cognitive event. It represents a reinterpretation of the current status of the visual hierarchy.

Animals↗
PubMed1999

Repetition priming and the time course of object recognition: an fMRI study.

We investigated the effects of repetition priming on the time course of recognition in several visual areas of the brain using fMRI. We slowed down recognition by gradually revealing the stimuli, in order to prolong the pre-recognition phase. Activation was lower for primed than for non-primed objects overall in both the occipitotemporal region (OTR) and the intraparietal region (IPR). A difference was found between primed and non-primed objects in the rate of increase of OTR activation. We concluded that the IPR, in addition to the OTR, was affected by repetition priming, and that this effect was different from that seen in the OTR.

Adult↗
PubMed2006

Coordinate transformations in object recognition.

A basic problem of visual perception is how human beings recognize objects after spatial transformations. Three central classes of findings have to be accounted for: (a) Recognition performance varies systematically with orientation, size, and position; (b) recognition latencies are sequentially additive, suggesting analogue transformation processes; and (c) orientation and size congruency effects indicate that recognition involves the adjustment of a reference frame. All 3 classes of findings can be explained by a transformational framework of recognition: Recognition is achieved by an analogue transformation of a perceptual coordinate system that aligns memory and input representations. Coordinate transformations can be implemented neurocomputationally by gain (amplitude) modulation and may be regarded as a general processing principle of the visual cortex.

Discrimination Learning↗
PubMed2001

Attentional guidance of the eyes by contextual information and abrupt onsets.

Contextual cuing is a memory-based phenomenon in which previously encountered global pattern information in a display can automatically guide attention to the location of a target (Chun & Jiang, 1998), leading to rapid and accurate responses. What is not clear is how contextual cuing works. By monitoring eye movements, we investigated the roles that recognition and guidance play in contextual cuing. Recognition does not appear to occur on every trial and sometimes does not have its effects until later in the search process. When recognition does occur, attention is guided straight to the target rather than in the general direction. In Experiment 2, we investigated the interaction between memory-driven search (contextual cuing) and stimulus-driven attentional capture by abrupt onsets. Contextual cuing was able to override capture by abrupt onsets. In contrast, onsets had almost no effect on the degree of contextual cuing. These data are discussed in terms of the role of top-down and bottom-up factors in the guidance of attention in visual search.

Adult↗
PubMed2001

Generation of oculomotor images during tasks requiring visual recognition of polygons.

This paper concerns the contribution of mentally simulated ocular exploration to generation of a visual mental image. In Exp. 1, repeated exploration of the outlines of an irregular decagon allowed an incidental learning of the shape. Analyses showed subjects memorized their ocular movements rather than the polygon. In Exp. 2, exploration of a reversible figure such as a Necker cube varied in opposite directions. Then, both perspective possibilities are presented. The perspective the subjects recognized depended on the way they explored the ambiguous figure. In both experiments, during recognition the subjects recalled a visual mental image of the polygon they compared with the different polygons proposed for recognition. To interpret the data, hypotheses concerning common processes underlying both motor intention of ocular movements and generation of a visual image are suggested.

Adult↗
PubMed1976

Visual discrimination in monkey with removal of inferotemporal cortex.

The monkey with removal of the inferotemporal cortex (IT monkey) showed a marked impairment of discrimination between a pair of visual pattern stimuli, which consisted of different patterns on the identical background [corrected] plaques. The present study showed that an IT monkey, unlike an unoperated normal monkey, performed discrimination with utilizing a partial cue within the whole configuration of pattern stimuli. In contrast to a general concept, the present finding appears to raise a question as to whether the IT monkey can perceive or identify visual pattern.

Animals↗
PubMedDate not supplied

Visual performance of adults with prelingual auditory impairment.

Reaction times and picture evaluations by 18 adults with hearing loss were compared with those of 18 matched controls during two visual priming tasks. In Task 1, participants reacted to sexual and plant target pictures (while influenced by similar preceding pictures) by pressing "sex" or "plant" buttons. In Task 2, they evaluated target Japanese ideographs (while influenced by preceding positive or negative facial expressions as prime pictures) by pressing "positive" or "negative" buttons. In Task 1, the controls had the faster responses. In Task 2, they showed the usual congruent priming effect during very short prime presentations. Participants with hearing loss showed this effect only during short and long prime presentation times; thus, they were not superior to the controls in picture recognition, instead showing (a) impaired processing of visual information or (b) impaired perceptual-motor skills regarding quick responses to visual information (or both).

Adult↗
PubMed1990

Verbal overshadowing of visual memories: some things are better left unsaid.

It is widely believed that verbal processing generally improves memory performance. However, in a series of six experiments, verbalizing the appearance of previously seen visual stimuli impaired subsequent recognition performance. In Experiment 1, subjects viewed a videotape including a salient individual. Later, some subjects described the individual's face. Subjects who verbalized the face performed less well on a subsequent recognition test than control subjects who did not engage in memory verbalization. The results of Experiment 2 replicated those of Experiment 1 and further clarified the effect of memory verbalization by demonstrating that visualization does not impair face recognition. In Experiments 3 and 4 we explored the hypothesis that memory verbalization impairs memory for stimuli that are difficult to put into words. In Experiment 3 memory impairment followed the verbalization of a different visual stimulus: color. In Experiment 4 marginal memory improvement followed the verbalization of a verbal stimulus: a brief spoken statement. In Experiments 5 and 6 the source of verbally induced memory impairment was explored. The results of Experiment 5 suggested that the impairment does not reflect a temporary verbal set, but rather indicates relatively long-lasting memory interference. Finally, Experiment 6 demonstrated that limiting subjects' time to make recognition decisions alleviates the impairment, suggesting that memory verbalization overshadows but does not eradicate the original visual memory. This collection of results is consistent with a recording interference hypothesis: verbalizing a visual memory may produce a verbally biased memory representation that can interfere with the application of the original visual memory.

Cues↗