Hemispheric asymmetry for spatially filtered stimuli belonging to different semantic categories

How semantic category modulates preschool children's visual memory

The dynamic interplay between perception and memory has been explored in preschool children by presenting filtered stimuli regarding animals and artifacts. The identification of filtered images was markedly influenced by both prior exposure and the semantic nature of the stimuli. The identification of animals required less physical information than artifacts did. Our results corroborate the notion that the human attention system evolves to reliably develop definite category-specific selection criteria by which living entities are monitored in different ways.

Revisiting domain-general accounts of category specificity in mind and brain

Theories about the neural basis of semantic knowledge have been strongly influenced by reports that particular semantic categories can be differentially impaired by neuropathology and can differentially activate particular regions of cortex in brain imaging studies. One well-known interpretation of these data is that the brain has evolved distinct functional and anatomical modules for storing and retrieving knowledge about different kinds of things. We review the evidence supporting an alternative view: that category specificity arises from many heterogeneous factors and so tells us little directly about the cognitive and neural architecture of semantic memory. We consider four general hypotheses about domain-general causes of category-specific patterns, their roots in early work, and their reemergence in contemporary research. We argue that there is compelling evidence supporting each hypothesis, and that the different hypotheses together can explain most of the interesting data. We further suggest that such a multifactor domain-general approach to category specificity is appealing partly because it explains the important findings with reference to theoretical claims that are already widely accepted, and partly because it resolves several puzzles that arise under the alternative view. For further resources related to this article, please visit the WIREs website.

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Ultra rapid object categorization: effects of level, animacy and context

It is widely agreed that in object categorization bottom-up and top-down influences interact. How top-down processes affect categorization has been primarily investigated in isolation, with only one higher level process at a time being manipulated. Here, we investigate the combination of different top-down influences (by varying the level of category, the animacy and the background of the object) and their effect on rapid object categorization. Subjects participated in a two-alternative forced choice rapid categorization task, while we measured accuracy and reaction times. Subjects had to categorize objects on the superordinate, basic or subordinate level. Objects belonged to the category animal or vehicle and each object was presented on a gray, congruent (upright) or incongruent (inverted) background. The results show that each top-down manipulation impacts object categorization and that they interact strongly. The best categorization was achieved on the superordinate level, providing no advantage for basic level in rapid categorization. Categorization between vehicles was faster than between animals on the basic level and vice versa on the subordinate level. Objects in homogenous gray background (context) yielded better overall performance than objects embedded in complex scenes, an effect most prominent on the subordinate level. An inverted background had no negative effect on object categorization compared to upright scenes. These results show how different top-down manipulations, such as category level, category type and background information, are related. We discuss the implications of top-down interactions on the interpretation of categorization results.

Acquired prosopagnosia with spared within-class object recognition but impaired recognition of degraded basic-level objects

We present a new case of acquired prosopagnosia resulting from extensive lesions predominantly in the right occipitotemporal cortex. Functional brain imaging revealed atypical activation of all core face areas in the right hemisphere, with reduced signal difference between faces and objects compared to controls. In contrast, Herschel's lateral occipital complex showed normal activation to objects. Behaviourally, Herschel is severely impaired with the recognition of familiar faces, discrimination between unfamiliar identities, and the perception of facial expression and gender. Notably, his visual recognition deficits are largely restricted to faces, suggesting that the damaged mechanisms are face-specific. He showed normal recognition memory for a wide variety of object classes in several paradigms, normal ability to discriminate between highly similar items within a novel object category, and intact ability to name basic objects (except four-legged animals). Furthermore, Herschel displayed a normal face composite effect and typical global advantage and global interference effects in the Navon task, suggesting spared integration of both face and nonface information. Nevertheless, he failed visual closure tests requiring recognition of basic objects from degraded images. This abnormality in basic object recognition is at odds with his spared within-class recognition and presents a challenge to hierarchical models of object perception.

Temporal dynamics of memory-related effects in older and young adults: an event-related potential study

Priming effects on the identification process were examined in young and older adults by using event-related potentials (ERPs). Animals and artifacts were presented in an ascending sequence of filtered images, half of which had been shown in their complete versions in a previous study phase. Each stimulus was represented by a progressively less filtered image (i.e., more complete) until the whole version was revealed in a sequence of frames. Such a paradigm allowed us to record ERPs prior to, and during, the identification of stimuli. Results showed a dynamic interplay between memory, category, and aging effects. At the moment of identification, young adults elicited larger positivity at parietal sites for previously studied stimuli and this effect was not observed for older adults. For stimuli previously studied, a striking effect was observed in both groups at the level just prior to overt identification. In addition, a frontally distributed priming effect was evident in the elderly. Category-related ERP differences emerged between the two age groups. In particular, younger participants elicited an early positive activation at anterior sites upon seeing stimuli of animals. These results are discussed in relation to current models of recognition memory, categorization, and age-related cognitive decline.

Stimulus type, level of categorization, and spatial-frequencies utilization: implications for perceptual categorization hierarchies

The type of visual information needed for categorizing faces and nonface objects was investigated by manipulating spatial frequency scales available in the image during a category verification task addressing basic and subordinate levels. Spatial filtering had opposite effects on faces and airplanes that were modulated by categorization level. The absence of low frequencies impaired the categorization of faces similarly at both levels, whereas the absence of high frequencies was inconsequential throughout. In contrast, basic-level categorization of airplanes was equally impaired by the absence of either low or high frequencies, whereas at the subordinate level, the absence of high frequencies had more deleterious effects. These data suggest that categorization of faces either at the basic level or by race is based primarily on their global shape but also on the configuration of details. By contrast, basic-level categorization of objects is based on their global shape, whereas category-specific diagnostic details determine the information needed for their subordinate categorization. The authors conclude that the entry point in visual recognition is flexible and determined conjointly by the stimulus category and the level of categorization, which reflects the observer's recognition goal.

Category-specificity in visual object recognition

Are all categories of objects recognized in the same manner visually? Evidence from neuropsychology suggests they are not: some brain damaged patients are more impaired in recognizing natural objects than artefacts whereas others show the opposite impairment. Category-effects have also been demonstrated in neurologically intact subjects, but the findings are contradictory and there is no agreement as to why category-effects arise. This article presents a pre-semantic account of category-effects (PACE) in visual object recognition. PACE assumes two processing stages: shape configuration (the binding of shape elements into elaborate shape descriptions) and selection (among competing representations in visual long-term memory), which are held to be differentially affected by the structural similarity between objects. Drawing on evidence from clinical studies, experimental studies with neurologically intact subjects and functional imaging studies, it is argued that PACE can account for category-effects at both behavioural and neural levels in patients and neurologically intact subjects. The theory also accounts for the way in which category-effects are affected by different task parameters (the degree of perceptual differentiation called for), stimulus characteristics (whether stimuli are presented as silhouettes, full line-drawings, or fragmented forms), stimulus presentation (stimulus exposure duration and position) as well as interactions between these parameters.

Differential Lateralization for Words and Faces: Category or Psychophysics?

This set of three experiments assessed the influence of different psychophysical factors on the lateralization of the N170 event-related potential (ERP) component to words and faces. In all experiments, words elicited a left-lateralized N170, whereas faces elicited a right-lateralized or nonlateralized N170 depending on presentation conditions. Experiment 1 showed that lateralization for words (but not for faces) was influenced by spatial frequency. Experiment 2 showed that stimulus presentation time influenced N170 lateralization independently of spatial frequency composition. Finally, Experiment 3 showed that stimulus size and resolution did not influence N170 lateralization, but did influence N170 amplitude, albeit differentially for words and faces. These findings suggest that differential lateralization for words and faces, at least as measured by the N170, is influenced by spatial frequency (words), stimulus presentation time, and category.

Recognition of category-related visual stimuli in Parkinson's disease: Before and after pharmacological treatment

Visual-sensory dysfunctions and semantic processing impairments are widely reported in Parkinson's disease (PD) research. The present study investigated the category-specific deficit in object recognition as a function of both the semantic category and spatial frequency content of stimuli. In the first experiment, the role of dopamine in object-recognition processing was assessed by comparing PD drug naïve (PD-DN), PD receiving levodopa treatment (PD-LD), and control subjects. Experiment 2 consisted of a retest session for PD drug naïve subjects after a period of pharmacological treatment. All participants completed an identification task which displayed animals and tools at nine levels of filtering. Each object was revealed in a sequence of frames whereby the object was presented at increasingly less-filtered images up to a complete version of the image. Results indicate an impaired identification pattern for PD-DN subjects solely for animal category stimuli. This differential pharmacological therapy effect was also confirmed at retest (experiment 2). Thus, our data suggest that dopaminergic loss has a specific role in category-specific impairment. Two possible hypotheses are discussed that may account for the defective recognition of semantically different objects in PD.

Category-specific visual recognition as affected by aging and expertise

The influence of aging and expertise on visual identification as function of semantic category (animals and tools) and spatial-frequency content of stimuli was investigated. Three-age groups of experts (whose profession required the use of manipulable tools) and non-experts, participated to the experiment. Data showed a different involvement of low and high spatial-frequency channels in processing objects semantically different: animals were identified at a coarse spatial scale (low spatial frequencies) and tools at a finer spatial scale (higher spatial frequencies). A gradual age-related decline in the identification for both categories (more physical information was required as the age increased) was found in non-experts, while in experts a similar trend was found only for animals and not for tools. In fact, independently on the age, experts could identify tools without requiring more visual details, probably for the benefits from their long-term experience with tools. Expertise, represented at higher levels of cognitive processing, might compensate the loss of lower levels of information processing due to aging.

Hippocampus proper distinguishes between identified and unidentified real-life visual objects: an intracranial ERP study

Converging evidence indicates that the medial temporal lobe participates not only in memory but also in visual object processing. We investigated hippocampal contributions to visual object identification by recording event-related potentials directly from within the hippocampus during a visual object identification task with spatially filtered pictures of real objects presented at different levels of filtering. Hippocampal responses differentiated between identified and unidentified visual objects within a time window of 200-900 ms after stimulus presentation: identified objects elicited a small negative component peaking around 300 ms (hippocampal-N300) and a large positive component, around 650 ms (hippocampal-P600), while the N300 was increased and the P600 was reduced in amplitude in response to unidentified objects. These findings demonstrate that the hippocampus proper contributes to the identification of visual objects discriminating from the very early between identified and unidentified meaningful visual objects.

A New Standardized Set of Ecological Pictures for Experimental and Clinical Research on Visual Object Processing

A new set of 174 pictures in black-and-white, coloured and spatially filtered versions, taken from photographs of real objects belonging to different semantic categories, was realised for experimental and clinical research on visual object processing. Two samples, one of English speakers and one of Italian speakers, were tested in order to provide the normative data for each picture, in both black-and-white and coloured versions, in relation to familiarity, visual complexity and name agreement.