An attenuation of the 'normal' category effect in patients with Alzheimer's disease: a review and bootstrap analysis

There is a consensus that Alzheimer's disease (AD) impairs semantic information, with one of the first markers being anomia i.e. an impaired ability to name items. Doubts remain, however, about whether this naming impairment differentially affects items from the living and nonliving knowledge domains. Most studies have reported an impairment for naming living things (e.g. animals or plants), a minority have found an impairment for nonliving things (e.g. tools or vehicles), and some have found no category-specific effect. A survey of the literature reveals that this lack of agreement may reflect a failure to control for intrinsic variables (such as familiarity) and the problems associated with ceiling effects in the control data. Investigating picture naming in 32 AD patients and 34 elderly controls, we used bootstrap techniques to deal with the abnormal distributions in both groups. Our analyses revealed the previously reported impairment for naming living things in AD patients and that this persisted even when intrinsic variables were covaried; however, covarying control performance eliminated the significant category effect. Indeed, the within-group comparison of living and nonliving naming revealed a larger effect size for controls than patients. We conclude that the category effect in Alzheimer's disease is no larger than is expected in the healthy brain and may even represent a small diminution of the normal profile.     

Guided saccades modulate face- and body-sensitive activation in the occipitotemporal cortex during social perception

Functional magnetic resonance imaging (fMRI) has identified distinct brain regions in ventral occipitotemporal cortex (VOTC) and lateral occipitotemporal cortex (LOTC) that are differentially activated by pictures of faces and bodies. Recent work from our laboratory has shown that the strong LOTC activation evoked by bodies in which the face is occluded is attenuated when the occlusion is removed. We hypothesized that this attenuation may occur because subjects preferentially fixate upon faces when present in the scene. Here, we experimentally manipulated subjects’ fixations while they viewed a static picture of a character whose face, hand, and torso were continuously visible throughout each run. The subject’s saccades and fixations were guided by a small fixation cross that made discrete jumps to a new location every 500 ms. Subjects were instructed to follow the fixation cross and make a button press whenever it changed size. In a series of blocks, the fixation cross shifted from locations on the face, on the hand, and to locations on a background image of a phase-scrambled face. In a second study, the fixation cross moved similarly, but the hand locations were changed to locations along the character’s body or torso. A localizer task was used to identify face- and body-sensitive regions of LOTC. Body-sensitive regions were strongly activated when the subjects’ saccades were guided over the character’s torso relative to when the saccades were guided over the character’s face. Little to no activity occurred in the body-sensitive region of LOTC when the subjects’ saccades were guided over the character’s hand. The localizer task was unable to differentiate body-sensitive regions in lateral VOTC from face-sensitive regions, or body-sensitive regions in medial VOTC from flower-sensitive regions. Guided saccades over the body strongly activated both lateral and medial VOTC. These results provide new insights into the function of body-sensitive visual areas in both LOTC and VOTC, and illustrate the potential confounding influence of uncontrolled eye movements for neuroimaging studies of social perception.     

Now you see it,now you don't: The context dependent nature of category-effects in visual object recognition

In two experiments, we test predictions regarding processing advantages/disadvantages for natural objects and artefacts in visual object recognition. Varying three important parameters—degree of perceptual differentiation, stimulus format, and stimulus exposure duration—we show how different category-effects can be provoked in normal subjects on the same task. We interpret the results in light of the Pre-semantic Account of Category Effects (PACE; Gerlach, 2009), and conclude that category-effects do not reflect absolute processing differences between categories. Rather, category-effects are products of common operations which are differentially affected by the structural similarity among objects (with natural objects being more structurally similar than artefacts). The potentially most important aspect of the present study is the demonstration that category-effects are very context dependent; an aspect which has been neglected in earlier literature on category-specificity. PACE provides a useful framework in this respect, as it specifies how category-effects are influenced by changes in task and stimulus characteristics.     

Category-specific effects on the identification of non-manipulable objects

Theories of category-specific effects on visual object identification predict easier identification of non-living than living objects. The Sensory-Functional theory credits greater representational weighting of the visual properties of living objects independent of greater weighting of the functional properties of non-living objects. It predicts a lost or reversed non-living advantage for non-manipulable objects. Normal participants matched pictures of non-manipulable objects with words describing three levels of identity while visual object similarity, and concept familiarity were controlled. Consistent with the Sensory-Functional theory, living objects were matched faster than non-living objects. Concept familiarity facilitated subordinate matches. Visual similarity hampered subordinate matches and facilitated basic matches.     

Relative contributions of kind- and domain-level concepts to expectations concerning unfamiliar exemplars: Developmental change and domain differences

Two inferential routes allow children to produce expectations about new instances of ontological categories like “animal” and “artefact.” One is to generalise information from a “look-up table” of familiar kind-concepts. The other one is to use independent expectations at the level of ontological domains. Our experiment pits these two sources of information against each other, using a sentence-judgement task associating properties with images of familiar and unfamiliar artefacts and animals. “Strange” properties are compatible with the ontological concept, but not encountered in any familiar kind. A look-up strategy would lead children to reject them and an independent expectation strategy to accept them. In both domains, we find a difference in reaction to strange properties associated with familiar vs. unfamiliar items, which shows that even young children do use independent domain-level information. We also found a U-shaped curve in propensity to use such abstract information. In addition, animal categories are the object of much more definite domain-level expectations, which supports the notion that the animal domain is more causally integrated than the artefact domain.     

An examination of differential repetition priming effects for natural and man-made objects

It has been theorized that differential cognitive resources may be involved in the processing of information pertaining to natural and man-made categories, commonly referred to as category specificity. The present study used four experiments to assess whether a natural priming advantage exists and, if so, whether color, texture, color diagnosticity, object complexity, and familiarity could account for the categorical difference. To do so, a repetition priming paradigm was used in which masked primes were briefly presented, and targets were categorized as natural or man-made. Across four experiments, a greater degree of priming was observed for natural as opposed to man-made stimuli. Examination of stimulus characteristics that could account for the differences revealed that the natural priming advantage was in part driven by color diagnosticity and familiarity. Results of this study support the notion that different cognitive resources represent and/or are involved in the processing of natural and man-made categories.