Repetition suppression in occipital–temporal visual areas is modulated by physical rather than semantic features of objects

Feasibility study of functional near-infrared spectroscopy in the ventral visual pathway for real-life applications

Significance

fNIRS-based neuroenhancement depends on the feasible detection of hemodynamic responses in target brain regions. Using the lateral occipital complex (LOC) and the fusiform face area (FFA) in the ventral visual pathway as neurofeedback targets boosts performance in visual recognition. However, the feasibility of utilizing fNIRS to detect LOC and FFA activity in adults remains to be validated as the depth of these regions may exceed the detection limit of fNIRS.

Aim

This study aims to investigate the feasibility of using fNIRS to measure hemodynamic responses in the ventral visual pathway, specifically in the LOC and FFA, in adults.

Approach

We recorded the hemodynamic activities of the LOC and FFA regions in 35 subjects using a portable eight-channel fNIRS instrument. A standard one-back object and face recognition task was employed to elicit selective brain responses in the LOC and FFA regions. The placement of fNIRS optodes for LOC and FFA detection was guided by our group's transcranial brain atlas (TBA).

Results

Our findings revealed selective activation of the LOC target channel (CH2) in response to objects, whereas the FFA target channel (CH7) did not exhibit selective activation in response to faces.

Conclusions

Our findings indicate that, although fNIRS detection has limitations in capturing FFA activity, the LOC region emerges as a viable target for fNIRS-based detection. Furthermore, our results advocate for the adoption of the TBA-based method for setting the LOC target channel, offering a promising solution for optrode placement. This feasibility study stands as the inaugural validation of fNIRS for detecting cortical activity in the ventral visual pathway, underscoring its ecological validity. We suggest that our findings establish a pivotal technical groundwork for prospective real-life applications of fNIRS-based research.

A review of the impairments, preserved visual functions, and neuropathology in 21 patients with visual form agnosia - A unique defect with line drawings

We present a comprehensive review of the rare syndrome visual form agnosia (VFA). We begin by documenting its history, including the origins of the term, and the first case study labelled as VFA. The defining characteristics of the syndrome, as others have previously defined it, are then described. The impairments, preserved aspects of visual perception, and areas of brain damage in 21 patients who meet these defining characteristics are described in detail, including which tests were used to verify the presence or absence of key symptoms. From this, we note important similarities along with notable areas of divergence between patients. Damage to the occipital lobe (20/21), an inability to recognise line drawings (19/21), preserved colour vision (14/21), and visual field defects (16/21) were areas of consistency across most cases. We found it useful to distinguish between shape and form as distinct constructs when examining perceptual abilities in VFA patients. Our observations suggest that these patients often exhibit difficulties in processing simplified versions of form. Deficits in processing orientation and size were uncommon. Motion perception and visual imagery were not widely tested for despite being typically cited as defining features of the syndrome - although in the sample described, motion perception was never found to be a deficit. Moreover, problems with vision (e.g., poor visual acuity and the presence of hemianopias/scotomas in the visual fields) are more common than we would have thought and may also contribute to perceptual impairments in patients with VFA. We conclude that VFA is a perceptual disorder where the visual system has a reduced ability to synthesise lines together for the purposes of making sense of what images represent holistically.

The Effects of Word Identity, Case, and SOA on Word Priming in a Subliminal Context

It is widely assumed that subliminal word priming is case insensitive and that a short SOA (< 100 ms) is required to observe any effects. Here we attempted to replicate results from an influential study with the inclusion of a longer SOA to re-examine these assumptions. Participants performed a semantic categorisation task on visible word targets that were preceded either 64 or 192 ms by a subliminal prime. The prime and target were either the same or different word and could appear in the same or different case. We confirmed the presence of subliminal word priming (same word < different word reaction times). The word priming effect did not differ when case was the same or different, which supports case insensitive word priming. However, there was a general facilitation effect driven by case (same case < different case). Finally, there was a significant difference between the two SOA conditions; however, there were no interactions between SOA and any other factor, demonstrating that subliminal priming did not differ between short and long SOAs. The results demonstrate that word priming is case insensitive but that there is nevertheless an overall facilitation when words, regardless if they are repeated or not, are presented in the same case. This facilitation in case may reflect modularity in the low-level processing of the visual characteristics of words.

Task-Irrelevant Semantic Properties of Objects Impinge on Sensory Representations within the Early Visual Cortex

Objects can be described in terms of low-level (e.g., boundaries) and high-level properties (e.g., object semantics). While recent behavioral findings suggest that the influence of semantic relatedness between objects on attentional allocation can be independent of task-relevance, the underlying neural substrate of semantic influences on attention remains ill-defined. Here, we employ behavioral and functional magnetic resonance imaging measures to uncover the mechanism by which semantic information increases visual processing efficiency. We demonstrate that the strength of the semantic relatedness signal decoded from the left inferior frontal gyrus: 1) influences attention, producing behavioral semantic benefits; 2) biases spatial attention maps in the intraparietal sulcus, subsequently modulating early visual cortex activity; and 3) directly predicts the magnitude of behavioral semantic benefit. Altogether, these results identify a specific mechanism driving task-independent semantic influences on attention.

Incidental Verbal Semantic Processing Recruits the Fronto-temporal Semantic Control Network

The frontoparietal semantic network, encompassing the inferior frontal gyrus and the posterior middle temporal cortex, is considered to be involved in semantic control processes. The explicit versus implicit nature of these control processes remains however poorly understood. The present study examined this question by assessing regional brain responses to the semantic attributes of an unattended stream of auditory words while participants' top-down attentional control processes were absorbed by a demanding visual search task. Response selectivity to semantic aspects of verbal stimuli was assessed via a functional magnetic resonance imaging response adaptation paradigm. We observed that implicit semantic processing of an unattended verbal stream recruited not only unimodal and amodal cortices in posterior supporting semantic knowledge areas, but also inferior frontal and posterior middle temporal areas considered to be part of the semantic control network. These results indicate that frontotemporal semantic networks support incidental semantic (control) processes.

Repetition of Computer Security Warnings Results in Differential Repetition Suppression Effects as Revealed With Functional MRI

Computer users are often the last line of defense in computer security. However, with repeated exposures to system messages and computer security warnings, neural and behavioral responses show evidence of habituation. Habituation has been demonstrated at a neural level as repetition suppression where responses are attenuated with subsequent repetitions. In the brain, repetition suppression to visual stimuli has been demonstrated in multiple cortical areas, including the occipital lobe and medial temporal lobe. Prior research into the repetition suppression effect has generally focused on a single repetition and has not examined the pattern of signal suppression with repeated exposures. We used complex, everyday stimuli, in the form of images of computer programs or security warning messages, to examine the repetition suppression effect across repeated exposures. The use of computer warnings as stimuli also allowed us to examine the activation of learned fearful stimuli. We observed widespread linear decreases in activation with repeated exposures, suggesting that repetition suppression continues after the first repetition. Further, we found greater activation for warning messages compared to neutral images in the anterior insula, pre-supplemental motor area, and inferior frontal gyrus, suggesting differential processing of security warning messages. However, the repetition suppression effect was similar in these regions for both warning messages and neutral images. Additionally, we observed an increase of activation in the default mode network with repeated exposures, suggestive of increased mind wandering with continuing habituation.

Neuroimaging supports the representational nature of the earliest human engravings

The earliest human graphic productions, consisting of abstract patterns engraved on a variety of media, date to the Lower and Middle Palaeolithic. They are associated with anatomically modern and archaic hominins. The nature and significance of these engravings are still under question. To address this issue, we used functional magnetic resonance imaging to compare brain activations triggered by the perception of engraved patterns dating between 540 000 and 30 000 years before the present with those elicited by the perception of scenes, objects, symbol-like characters and written words. The perception of the engravings bilaterally activated regions along the ventral route in a pattern similar to that activated by the perception of objects, suggesting that these graphic productions are processed as organized visual representations in the brain. Moreover, the perception of the engravings led to a leftward activation of the visual word form area. These results support the hypothesis that these engravings have the visual properties of meaningful representations in present-day humans, and could have served such purpose in early modern humans and archaic hominins.

A pantomiming priming study on the grasp and functional use actions of tools

It has previously been demonstrated that tool recognition is facilitated by the repeated visual presentation of object features affording actions, such as those related to grasping and their functional use. It is unclear, however, if this can also facilitate pantomiming. Participants were presented with an image of a prime followed by a target tool and were required to pantomime the appropriate action for each one. The grasp and functional use attributes of the target tool were either the same or different to the prime. Contrary to expectations, participants were slower at pantomiming the target tool relative to the prime regardless of whether the grasp and function of the tool were the same or different-except when the prime and target tools consisted of identical images of the same exemplar. We also found a decrease in accuracy of performing functional use actions for the target tool relative to the prime when the two differed in functional use but not grasp. We reconcile differences between our findings and those that have performed priming studies on tool recognition with differences in task demands and known differences in how the brain recognises tools and performs actions to make use of them.

Perceptual Similarity Can Drive Age-Related Elevation of False Recognition

Older adults consistently show elevated rates of false recognition of new items that are related to studied items. This finding has been largely attributed to a greater tendency for older adults to rely on conceptual gist during memory recognition tasks. However, perceptual factors may also be implicated considering that related items are not only conceptually but also perceptually similar. While some findings do suggest that age-related increases in false recognitions can be driven by perceptual factors, little is known about the nature and circumstances under which these factors operate. To address this gap, we measured basic visual ability as well as false recognition for four different image categories (upright faces, inverted faces, chairs, houses) in younger (n = 34) and older (n = 34) adults. Each image category represented different levels of variability in perceptual similarity and pre-experimental exposure. Perceptual similarity was objectively defined on the basis of the low-level properties of the images. We found evidence that perceptual similarity can contribute to elevated rates of false recognition in older adults. Our results also suggest that declines in basic visual abilities influence elevated false recognition in older adults for perceptually similar but not perceptually dissimilar items. We conclude that both perceptual and conceptual similarity can drive age-related differences in false recognition.

fMRI evidence of aberrant neural adaptation for objects in schizophrenia and bipolar disorder

Functional magnetic resonance imaging (fMRI) adaptation (also known as fMRI repetition suppression) has been widely used to characterize stimulus selectivity in vivo, a fundamental feature of neuronal processing in the brain. We investigated whether SZ patients and BD patients show aberrant fMRI adaptation for object perception. About 52 SZ patients, 55 BD patients, and 53 community controls completed an object discrimination task with three conditions: the same object presented twice, two exemplars from the same category, and two exemplars from different categories. We also administered two functional localizer tasks. A region of interest analysis was employed to evaluate a priori hypotheses about the lateral occipital complex (LOC) and early visual cortex (EVC). An exploratory whole brain analysis was also conducted. In the LOC and EVC, controls showed the expected reduced fMRI responses to repeated presentation of the same objects compared with different objects (i.e., fMRI adaptation for objects, p < .001). SZ patients showed an adaptation effect that was significantly smaller compared with controls. BD patients showed a lack of fMRI adaptation. The whole brain analyses showed enhanced fMRI responses to repeated presentation of the same objects only in BD patients in several brain regions including anterior cingulate cortex. This study was the first to employ fMRI adaptation for objects in SZ and BD. The current findings provide empirical evidence of aberrant fMRI adaptation in the visual cortex in SZ and BD, but in distinctly different ways.

What Is Actually Affected by the Scrambling of Objects When Localizing the Lateral Occipital Complex?

The lateral occipital complex (LOC), the cortical region critical for shape perception, is localized with fMRI by its greater BOLD activity when viewing intact objects compared with their scrambled versions (resembling texture). Despite hundreds of studies investigating LOC, what the LOC localizer accomplishes—beyond distinguishing shape from texture—has never been resolved. By independently scattering the intact parts of objects, the axis structure defining the relations between parts was no longer defined. This led to a diminished BOLD response, despite the increase in the number of independent entities (the parts) produced by the scattering, thus indicating that LOC specifies interpart relations, in addition to specifying the shape of the parts themselves. LOC's sensitivity to relations is not confined to those between parts but is also readily apparent between objects, rendering it—and not subsequent “place” areas—as the critical region for the representation of scenes. Moreover, that these effects are witnessed with novel as well as familiar intact objects and scenes suggests that the relations are computed on the fly, rather than being retrieved from memory.

Occipitotemporal Category Representations Are Sensitive to Abstract Category Boundaries Defined by Generalization Demands

Categorization involves organizing perceptual information so as to maximize differences along dimensions that predict class membership while minimizing differences along dimensions that do not. In the current experiment, we investigated how neural representations reflecting learned category structure vary according to generalization demands. We asked male and female human participants to switch between two rules when determining whether stimuli should be considered members of a single known category. When categorizing according to the "strict" rule, participants were required to limit generalization to make fine-grained distinctions between stimuli and the category prototype. When categorizing according to the "lax" rule, participants were required to generalize category knowledge to highly atypical category members. As expected, frontoparietal regions were primarily sensitive to decisional demands (i.e., the distance of each stimulus from the active category boundary), whereas occipitotemporal representations were primarily sensitive to stimulus typicality (i.e., the similarity between each exemplar and the category prototype). Interestingly, occipitotemporal representations of stimulus typicality differed between rules. While decoding models were able to predict unseen data when trained and tested on the same rule, they were unable to do so when trained and tested on different rules. We additionally found that the discriminability of the multivariate signal negatively covaried with distance from the active category boundary. Thus, whereas many accounts of occipitotemporal cortex emphasize its important role in transforming visual information to accentuate learned category structure, our results highlight the flexible nature of these representations with regards to transient decisional demands.SIGNIFICANCE STATEMENT Occipitotemporal representations are known to reflect category structure and are often assumed to be largely invariant with regards to transient decisional demands. We found that representations of equivalent stimuli differed between strict and lax generalization rules, and that the discriminability of these representations increased as distance from abstract category boundaries decreased. Our results therefore indicate that occipitotemporal representations are flexibly modulated by abstract decisional factors.

The Lateral Occipital Complex shows no net response to object familiarity

In 1995, Malach et al. discovered an area whose fMRI BOLD response was greater when viewing intact, familiar objects than when viewing their scrambled versions (resembling texture). Since then hundreds of studies have explored this late visual region termed the Lateral Occipital Complex (LOC), which is now known to be critical for shape perception (James, Culham, Humphrey, Milner, & Goodale, 2003). Malach et al. (1995) discounted a role of familiarity by showing that “abstract” Henry Moore sculptures, unfamiliar to the subjects, also activated this region. This characterization of LOC as a region that responds to shape independently of familiarity has been accepted but never tested with control of the same low-level features. We assessed LOC's response to objects that had identical parts in two different arrangements, one familiar and the other novel. Malach was correct: There is no net effect of familiarity in LOC. However, a multivoxel correlation analysis showed that LOC does distinguish familiar from novel objects.

Selecting appropriate designs and comparison conditions in repetition paradigms

The studies described by Vogels (this issue) demonstrate the complexity of repetition effects in the visual processing stream. In addition to signal suppression, findings of inherited effects from earlier processing, and discrepancies between the stimulus selectivity of cells before and after repetition, have informed the inferences that can be drawn from measures over larger scales such as functional magnetic resonance imaging (fMRI) or electroencephalography (EEG). This work also demonstrates that integration of evidence across recording methods is vital for understanding repetition effects in the brain. It is however difficult to integrate evidence across different recording methods and repetition paradigms. At the crux of this difficulty is the selection of comparison or unrepeated stimulus conditions within paradigms, which influence the observed strength, selectivity and even direction of repetition effects. This viewpoint highlights prevalent methodological issues with regard to repeated-unrepeated stimulus comparisons: inherited adaptation, stimulus specific expectations, concurrent memory retrieval, stimulus novelty and familiarity, attention, and changes in neuronal selectivity with repetition. The extent to which current conflicting and uncertain findings are due to selection of unrepeated stimulus conditions is unknown, but needs to be addressed to develop models of repetition spanning recording methods and repetition paradigms.

Inborn and experience-dependent models of categorical brain organization. A position paper

The present review aims to summarize the debate in contemporary neuroscience between inborn and experience-dependent models of conceptual representations that goes back to the description of category-specific semantic disorders for biological and artifact categories. Experience-dependent models suggest that categorical disorders are the by-product of the differential weighting of different sources of knowledge in the representation of biological and artifact categories. These models maintain that semantic disorders are not really category-specific, because they do not respect the boundaries between different categories. They also argue that the brain structures which are disrupted in a given type of category-specific semantic disorder should correspond to the areas of convergence of the sensory-motor information which play a major role in the construction of that category. Furthermore, they provide a simple interpretation of gender-related categorical effects and are supported by studies assessing the importance of prior experience in the cortical representation of objects On the other hand, inborn models maintain that category-specific semantic disorders reflect the disruption of innate brain networks, which are shaped by natural selection to allow rapid identification of objects that are very relevant for survival. From the empirical point of view, these models are mainly supported by observations of blind subjects, which suggest that visual experience is not necessary for the emergence of category-specificity in the ventral stream of visual processing. The weight of the data supporting experience-dependent and inborn models is thoroughly discussed, stressing the fact observations made in blind subjects are still the subject of intense debate. It is concluded that at the present state of knowledge it is not possible to choose between experience-dependent and inborn models of conceptual representations.

The temporal dynamics of visual object priming

Priming reflects an important means of learning that is mediated by implicit memory. Importantly, priming occurs for previously viewed objects (item-specific priming) and their category relatives (category-wide priming). Two distinct neural mechanisms are known to mediate priming, including the sharpening of a neural object representation and the retrieval of stimulus-response mappings. Here, we investigated whether the relationship between these neural mechanisms could help explain why item-specific priming generates faster responses than category-wide priming. Participants studied pictures of everyday objects, and then performed a difficult picture identification task while we recorded event-related potentials (ERP). The identification task gradually revealed random line segments of previously viewed items (Studied), category exemplars of previously viewed items (Exemplar), and items that were not previously viewed (Unstudied). Studied items were identified sooner than Unstudied items, showing evidence of item-specific priming, and importantly Exemplar items were also identified sooner than Unstudied items, showing evidence of category-wide priming. Early activity showed sustained neural suppression of parietal activity for both types of priming. However, these neural suppression effects may have stemmed from distinct processes because while category-wide neural suppression was correlated with priming behavior, item-specific neural suppression was not. Late activity, examined with response-locked ERPs, showed additional processes related to item-specific priming including neural suppression in occipital areas and parietal activity that was correlated with behavior. Together, we conclude that item-specific and category-wide priming are mediated by separate, parallel neural mechanisms in the context of the current paradigm. Temporal differences in behavior are determined by the timecourses of these distinct processes.

The effects of the relationships between object features on multiple-identity tracking

Simultaneous tracking of multiple moving objects is essential in tasks such as traffic control, automobile driving, and scene surveillance. Recently, an increasing number of studies have focused on the roles of object identity and location binding in unique target tracking tasks, but contradictory results have been reported. In the present study, we introduced for the first time the Stroop stimuli of Chinese characters to the multiple-identity tracking paradigm, taking advantage of the ease to control the overall size, familiarity, and visual complexity of the Chinese characters. The results showed that when the observers were asked to track unique objects that bear two distinct features, the feature conflict disrupted the tracking performance, even when the given object has a distinctive identity. Our data revealed that the internal disaccord of semantic and physical features on an object can disturb the identity-location binding process in a multiple-identity tracking task, but does not affect the location information significantly.

Are reaction times obtained during fMRI scanning reliable and valid measures of behavior?

Assuming that behavior observed during functional magnetic resonance imaging (fMRI) is comparable with behavior outside the scanner appears to be a basic tenet in cognitive neuroscience. Nevertheless, this assumption has rarely been tested directly. Here, we examined the reliability and validity of speeded performance during fMRI scanning by having the same 30 participants perform a battery of five reaction time (RT) tasks in two separate fMRI sessions and a standard laboratory (i.e., outside-scanner) session. Medium-to-high intra-class correlations between the three sessions showed that individual RT differences were conserved across sessions. Thus, for the range of tasks used, test-retest reliability and criterion validity of performance during scanning were satisfactory. Further, the pattern of between-task relations did not change within the scanner, attesting to the construct validity of performance measurements during scanning. In some tasks, however, RTs obtained from fMRI conditions were significantly shorter than those observed under normal laboratory conditions. In summary, RTs obtained during fMRI scanning appear to be largely reliable and valid measures of behavior. The observed RT speed-up during scanning might reflect task-specific interactions with a slightly different neuro-cognitive state, indicating some limits to generalizing brain-behavior relations observed with fMRI. These findings encourage further efforts in fMRI research to establish the external validity of within-scanner task performance.

Category-selective attention modulates unconscious processes in the middle occipital gyrus

Many studies have revealed the top-down modulation (spatial attention, attentional load, etc.) on unconscious processing. However, there is little research about how category-selective attention could modulate the unconscious processing. In the present study, using functional magnetic resonance imaging (fMRI), the results showed that category-selective attention modulated unconscious face/tool processing in the middle occipital gyrus (MOG). Interestingly, MOG effects were of opposed direction for face and tool processes. During unconscious face processing, activation in MOG decreased under the face-selective attention compared with tool-selective attention. This result was in line with the predictive coding theory. During unconscious tool processing, however, activation in MOG increased under the tool-selective attention compared with face-selective attention. The different effects might be ascribed to an interaction between top-down category-selective processes and bottom-up processes in the partial awareness level as proposed by Kouider, De Gardelle, Sackur, and Dupoux (2010). Specifically, we suppose an "excessive activation" hypothesis.

Stimulus-response bindings code both abstract and specific representations of stimuli: evidence from a classification priming design that reverses multiple levels of response representation

Repetition priming can be caused by the rapid retrieval of previously encoded stimulus–response (S–R) bindings. S–R bindings have recently been shown to simultaneously code multiple levels of response representation, from specific Motor-actions to more abstract Decisions (“yes”/”no”) and Classifications (e.g., “man-made”/”natural”). Using an experimental design that reverses responses at all of these levels, we assessed whether S–R bindings also code multiple levels of stimulus representation. Across two experiments, we found effects of response reversal on priming when switching between object pictures and object names, consistent with S–R bindings that code stimuli at an abstract level. Nonetheless, the size of this reversal effect was smaller for such across-format (e.g., word–picture) repetition than for within-format (e.g., picture–picture) repetition, suggesting additional coding of format-specific stimulus representations. We conclude that S–R bindings simultaneously represent both stimuli and responses at multiple levels of abstraction.

Object representations in ventral and dorsal visual streams: fMRI repetition effects depend on attention and part-whole configuration

The effects of attention and object configuration on the neural responses to short-lag visual image repetition were investigated with fMRI. Attention to one of two object images in a prime display was cued spatially. The images were either intact or split vertically; a manipulation that negates the influence of view-based representations. A subsequent single intact probe image was named covertly. Behavioural priming observed as faster button presses was found for attended primes in both intact and split configurations, but only for uncued primes in the intact configuration. In a voxel-wise analysis, fMRI repetition suppression (RS) was observed in a left mid-fusiform region for attended primes, both intact and split, whilst a right intraparietal region showed repetition enhancement (RE) for intact primes, regardless of attention. In a factorial analysis across regions of interest (ROIs) defined from independent localiser contrasts, RS for attended objects in the ventral stream was significantly left-lateralised, whilst repetition effects in ventral and dorsal ROIs correlated with the amount of priming in specific conditions. These fMRI results extend hybrid theories of object recognition, implicating left ventral stream regions in analytic processing (requiring attention), consistent with prior hypotheses about hemispheric specialisation, and implicating dorsal stream regions in holistic processing (independent of attention).

Concordance between perceptual and categorical repetition effects in the ventral visual stream

The process of object categorization is an integral part of human cognition. In the present study, we have used a repetition suppression paradigm to determine the degree to which the ventral visual cortex is sensitive to categorical relationships. By using images of animals and tools, suppression across perceptual (stimulus level) and categorical repetitions (basic level and domain level) was compared and contrasted across the domain-selective and hierarchical organization of the ventral visual stream. Both perceptual and categorical repetition effects were insensitive to domain-selective tuning, with suppression most prominent in regions responding maximally to images, irrespective of stimulus domain. Likewise, both perceptual and categorical repetition produced overlapping suppression across multiple regions of the visual hierarchy. Some divergent patterns were observed. The right superior temporal sulcus demonstrated repetition suppression only at the basic level (different examples of the same basic object), and the right anterior fusiform gyrus was sensitive to direct stimulus repetition but not basic-level categorical repetition. Because of the high concordance between the response profiles of perceptual and categorical repetition effects, we conclude they arise from a common cognitive mechanism.

The role of apparent size in building- and object-specific regions of ventral visual cortex

Images of buildings and manipulable objects have been found to activate distinct regions in the ventral visual pathway. Yet, many non-categorical properties distinguish buildings from common everyday objects, and perhaps the most salient of these is size. In this fMRI study, we investigated whether or not changes in perceived scale can account for some of the differences in category-specific responses, independent of the influence of semantic or retinotopic image properties. We used independent scans to localize object-specific ROIs in lateral occipital cortex (LO) and scene-specific ROIs in the parahippocampal place area (PPA) and posterior collateral sulcus. We then contrasted the effects of stimulus category and perceived size/distance in these regions in a factorial design. Participants performed an oddball detection task while viewing images of objects, buildings, and planar rectangles both with and without a background that indicated stimulus size/distance via simple pictorial cues. The analyses of fMRI responses showed effects of perceived size/distance in addition to effects of category in LO and the PPA. Interestingly, when simple rectangles were presented in a control condition against the background that indicated size/distance, LO in the right hemisphere responded significantly more to the small/close rectangles than to the large/far ones, in spite of the fact that the rectangles themselves were identical. These findings suggest that ventral stream regions that show category specificity are modulated by the perceived size and distance of visual stimuli.

Hemispheric differences in specificity effects in talker identification

In the visual domain, Marsolek and colleagues (1999, 2008) have found support for two dissociable and parallel neural subsystems underlying object and shape recognition: an abstract-category subsystem that operates more effectively in the left cerebral hemisphere (LH), and a specific-exemplar subsystem that operates more effectively in the right cerebral hemisphere (RH). Evidence of this asymmetry has been observed in priming specificity for linguistic (words, pseudoword forms) and nonlinguistic (objects) stimuli. In the auditory domain, the authors previously found hemispheric asymmetries in priming effects for linguistic (spoken words) and nonlinguistic (environmental sounds) stimuli. In the present study, the same asymmetrical pattern was observed in talker identification by means of two long-term repetition-priming experiments. Both experiments consisted of a familiarization phase and a final talker identification test phase, using sentences as stimuli. The results showed that specificity effects (an advantage for same-sentence priming, relative to different-sentence priming) emerged when the target stimuli were presented to the left ear (RH), but not when the target stimuli were presented to the right ear (LH). Taken together, this consistent asymmetrical pattern of data from both domains-visual and auditory-may be indicative of a more general property of the human perceptual processing system. Theoretical implications are discussed.

What have We Learned from "Perturbing" the Human Cortical Motor System with Transcranial Magnetic Stimulation?

The purpose of this paper is twofold. First, we will review different approaches that one can use with transcranial magnetic stimulation (TMS) to study both its effects on motor behavior and on neural connections in the human brain. Second, we will present evidence obtained in TMS-based studies showing that the dorsal premotor area (PMd), the ventral premotor area (PMv), the supplementary motor area (SMA), and the pre-supplementary motor area (pre-SMA) each have different roles to play in motor behavior. We highlight the importance of the PMd in response selection based on arbitrary cues and in the control of arm movements, the PMv in grasping and in the discrimination of bodily actions, the SMA in movement sequencing and in bimanual coordination, and the pre-SMA in cognitive control. We will also discuss ways in which TMS can be used to chart “true” cerebral reorganization in clinical populations and how TMS might be used as a therapeutic tool to facilitate motor recovery after stroke. We will end our review by discussing some of the methodological challenges and future directions for using this tool in basic and clinical neuroscience.

Repetition suppression in occipitotemporal cortex despite negligible visual similarity: evidence for postperceptual processing?

The reduced neural response in certain brain regions when a task-relevant stimulus is repeated ("repetition suppression", RS) is often attributed to facilitation of the cognitive processes performed in those regions. Repetition of visual objects is associated with RS in the ventral and lateral occipital/temporal regions, and is typically attributed to facilitation of visual processes, ranging from the extraction of shape to the perceptual identification of objects. In two fMRI experiments using a semantic classification task, we found RS in a left lateral occipital/inferior temporal region to a picture of an object when the name of that object had previously been presented in a separate session. In other words, we found RS despite negligible visual similarity between the initial and repeated occurrences of an object identity. There was no evidence that this RS was driven by the learning of task-specific responses to an object identity ("S-R learning"). We consider several explanations of this occipitotemporal RS, such as phonological retrieval, semantic retrieval, and visual imagery. Although no explanation if fully satisfactory, it is proposed that such effects most plausibly relate to the extraction of task-relevant information relating to object size, either through the extraction of sensory-specific semantic information or through visual imagery processes. Our findings serve to emphasize the potential complexity of processing within traditionally visual regions, at least as measured by fMRI.

The cognitive neuroscience of prehension: recent developments

Prehension, the capacity to reach and grasp, is the key behavior that allows humans to change their environment. It continues to serve as a remarkable experimental test case for probing the cognitive architecture of goal-oriented action. This review focuses on recent experimental evidence that enhances or modifies how we might conceptualize the neural substrates of prehension. Emphasis is placed on studies that consider how precision grasps are selected and transformed into motor commands. Then, the mechanisms that extract action relevant information from vision and touch are considered. These include consideration of how parallel perceptual networks within parietal cortex, along with the ventral stream, are connected and share information to achieve common motor goals. On-line control of grasping action is discussed within a state estimation framework. The review ends with a consideration about how prehension fits within larger action repertoires that solve more complex goals and the possible cortical architectures needed to organize these actions.

The lateral-occipital and the inferior-frontal cortex play different roles during the naming of visually presented objects

We reasoned that if an area is devoted to processing only the visual features of objects, then transcranial magnetic stimulation (TMS) applied to this area in either hemisphere would affect the naming of objects presented in contralateral but not ipsilateral space. In contrast, if an area is involved in language, then one might expect to see effects of TMS when applied over the left but not the right hemisphere, regardless whether objects are in contralateral or ipsilateral space. Our experiments reveal two important findings. First, TMS delivered to the lateral-occipital complex (LOC), a visual-form area, affected the naming of objects presented in contralateral but not ipsilateral space, independent of which hemisphere was stimulated. In two additional experiments, when participants named the color of objects or made judgments about the size of stimuli as shown physically on a computer screen, TMS over the contralateral LOC did not affect color naming but did affect the participants' ability to make size judgments. Second, TMS delivered to the left but not the right posterior inferior-frontal gyrus (pIFG) affected the naming of objects irrespective of whether objects were presented in contralateral or ipsilateral space. In a separate experiment, when participants were asked to either read or categorize words, TMS over the left but not the right pIFG affected word categorization but not word reading. On the basis of these findings, we propose that when people name visually-presented objects, LOC processes the visual form of objects while the left pIFG processes the semantics of objects.

Category-specific neural processing for naming pictures of animals and naming pictures of tools: an ALE meta-analysis

Using activation-likelihood estimation (ALE) meta-analysis, we identified brain areas that are invoked when people name pictures of animals and pictures of tools. We found that naming animals and naming tools invoked separate distributed networks in the brain. Specifically, we found that naming animals invoked greater responses than naming tools in frontal lobe structures that are typically modulated by emotional content and task demands, and in a number of visual areas in the ventral stream. In contrast, naming tools invoked greater responses in a different set of areas in the ventral stream than those invoked by naming animals. Naming tools also invoked greater responses than naming animals in motor areas in the frontal lobe as well as in sensory areas in the parietal lobe. The only overlapping sites of activation that we found for naming these two categories of objects were in the left pars triangularis, the left inferior temporal gyrus, and the left parahippocampal gyrus. Taken together, our meta-analysis reveals that animals and tools are categorically represented in visual areas but show convergence in higher-order associative areas in the temporal and frontal lobes in regions that are typically regarded as being involved in memory and/or semantic processing. Our results also reveal that naming tools not only engages visual areas in the ventral stream but also a fronto-parietal network associated with tool use. Whether or not this network associated with tool use contributes directly to recognition will require further investigation.

FMRI adaptation during performance of learned arbitrary visuomotor conditional associations

In everyday life, people select motor responses according to arbitrary rules. For example, our movements while driving a car can be instructed by color cues that we see on traffic lights. These stimuli do not spatially relate to the actions that they specify. Associations between these stimuli and actions are called arbitrary visuomotor conditional associations. Earlier fMRI studies have tried to dissociate the sensory and motor components of these associations by introducing delays between the presentation of arbitrary cues and go-signals that instructed participants to perform actions. This approach, however, also introduces neural processes that are not necessarily related to the normal real-time production of arbitrary visuomotor responses, such as working memory and the suppression of motor responses. We used fMRI adaptation as an alternative approach to dissociate sensory and motor components. We found that visual areas in the occipital-temporal cortex adapted only to the presentation of arbitrary visual cues whereas a number of sensorimotor areas adapted only to the production of response. Visual areas in the occipital-temporal cortex do not have any known connections with parts of the brain that can control hand musculature. Therefore, it is conceivable that the brain areas that we report as having adapted to both stimulus presentation and response production (namely, the dorsal premotor area, the supplementary motor area, the cingulate, the anterior intra-parietal sulcus area, and the thalamus) are involved in the multiple steps between processing visual stimuli and activating the motor commands that these cues specify.

Adaptation to objects in the lateral occipital complex (LOC): shape or semantics?

A change in the basic-level class when viewing a sequence of two objects produces a large release from adaptation in LOC compared to when the images are identical. Is this due to a change in semantics or shape? In an fMRI-adaptation experiment, subjects viewed a sequence of two objects and judged whether the stimuli were identical in shape. Different-shaped stimuli could be from the same or different basic-level classes, where the physical similarities of the pairs in the two conditions were equated by a model of simple cell similarity. BOLD responses in LOC for the two conditions were equivalent, and higher than that of the identical condition, indicating that LOC is sensitive to shape rather than to basic-level semantics.

Electrophysiological evidence for size invariance in masked picture repetition priming

This experiment examined invariance in object representations through measuring event-related potentials (ERPs) to pictures in a masked repetition priming paradigm. Pairs of pictures were presented where the prime was either the same size or half the size of the target object and the target was either presented in a normal orientation or was a normal sized mirror reflection of the prime object. Previous masked repetition priming studies have found a cascade of priming effect sensitive to perceptual (N190/P190) and semantic (N400) properties of the stimulus. This experiment found that both early (N190/P190 effects) and later effects (N400) were invariant to size, whereas only the N190/P190 effect was invariant to mirror reflection. The combination of a small prime and a mirror reflected target led to no significant priming effects. Taken together, the results of this set of experiments suggests that object recognition, more specifically, activating an object representation, occurs in a hierarchical fashion where overlapping perceptual information between the prime and target is necessary, although not always sufficient, to activate a higher level semantic representation.