Stimulus features coded by single neurons of a macaque body category selective patch

Body category-selective regions of the primate temporal cortex respond to images of bodies, but it is unclear which fragments of such images drive single neurons’ responses in these regions. Here we applied the Bubbles technique to the responses of single macaque middle superior temporal sulcus (midSTS) body patch neurons to reveal the image fragments the neurons respond to. We found that local image fragments such as extremities (limbs), curved boundaries, and parts of the torso drove the large majority of neurons. Bubbles revealed the whole body in only a few neurons. Neurons coded the features in a manner that was tolerant to translation and scale changes. Most image fragments were excitatory but for a few neurons both inhibitory and excitatory fragments (opponent coding) were present in the same image. The fragments we reveal here in the body patch with Bubbles differ from those suggested in previous studies of face-selective neurons in face patches. Together, our data indicate that the majority of body patch neurons respond to local image fragments that occur frequently, but not exclusively, in bodies, with a coding that is tolerant to translation and scale. Overall, the data suggest that the body category selectivity of the midSTS body patch depends more on the feature statistics of bodies (e.g., extensions occur more frequently in bodies) than on semantics (bodies as an abstract category).The body category-selective regions in the human occipito-temporal cortex are defined as those that respond to images of bodies (1–8). We previously identified two bilateral regions in the macaque inferotemporal cortex that respond stronger to monkey, human, and animal bodies in comparison with other stimuli, including faces (6). Subsequent single-unit recordings in the posterior body patch [i.e., the middle superior temporal sulcus (midSTS) body patch] demonstrated that indeed the average spiking activity of the neuron population was greater to images of bodies compared with other objects. However, the responses of single neurons showed a strong selectivity for particular body—and sometimes nonbody—images (7). However, it is still unknown what particular stimulus features single body patch neurons respond to. Moreover, we still do not know how those neurons code information about different animate and inanimate stimuli.The Bubbles technique (9), in which parts of the image of an object are sampled by trial-unique randomly positioned Gaussian apertures, has been used successfully in many psychophysical studies to reveal the features critical for certain perceptual tasks such as face identification, gender discrimination, emotional discrimination, and so forth (e.g., refs. 9–13). Although this technique has been used in neuroimaging [functional MRI (fMRI), EEG, magnetoencephalography (MEG), and electrocorticography] studies (11, 12, 14), it has rarely been exploited in single-unit studies (15, 16), and this only for face stimuli.Here, we used the Bubbles technique to reveal the image fragments that drive single midSTS body patch neurons. Bubbles provides an unbiased method for sampling the images with the advantage that it requires no prior specification of stimulus features to which the neurons are supposed to be selective. With fMRI, we first defined the midSTS body patch in two monkeys. Then, in this identified body patch we recorded the spiking activity of well-isolated single neurons in response to 100 images of various categories. Based on the spiking activity to the 100 images, we selected for each neuron a response-eliciting image. Then, we sampled the selected image at five different spatial scales with randomly positioned Gaussian apertures and recorded the responses of the neuron to a large number of these trial-unique Bubbles stimuli. Following the experiment, we applied reverse correlation to relate the excitatory and inhibitory neural responses to particular image fragments.Furthermore, we assessed whether the revealed image fragments tolerated changes in spatial location and size of the Bubbles stimuli or instead reflected spatially localized image regions. We showed before that many midSTS body patch neurons respond to silhouettes of bodies (17). Silhouettes isolate shape contours, removing texture and shading information. Thus, in a subset of neurons, we applied Bubbles to a silhouette version of the selected image.     

Life motion signals lengthen perceived temporal duration

Point-light biological motions, conveying various different attributes of biological entities, have particular spatiotemporal properties that enable them to be processed with remarkable efficiency in the human visual system. Here we demonstrate that such signals automatically lengthen their perceived temporal duration independent of global configuration and without observers' subjective awareness of their biological nature. By using a duration discrimination paradigm, we showed that an upright biological motion sequence was perceived significantly longer than an inverted but otherwise identical sequence of the same duration. Furthermore, this temporal dilation effect could be extended to spatially scrambled biological motion signals, whose global configurations were completely disrupted, regardless of whether observers were aware of the nature of the stimuli. However, such an effect completely disappeared when critical biological characteristics were removed. Taken together, our findings suggest a special mechanism of time perception tuned to life motion signals and shed new light on the temporal encoding of biological motion.     

Atypical brain activation patterns during a face‐to‐face joint attention game in adults with autism spectrum disorder

Joint attention behaviors include initiating one's own and responding to another's bid for joint attention to an object, person, or topic. Joint attention abilities in autism are pervasively atypical, correlate with development of language and social abilities, and discriminate children with autism from other developmental disorders. Despite the importance of these behaviors, the neural correlates of joint attention in individuals with autism remain unclear. This paucity of data is likely due to the inherent challenge of acquiring data during a real‐time social interaction. We used a novel experimental set‐up in which participants engaged with an experimenter in an interactive face‐to‐face joint attention game during fMRI data acquisition. Both initiating and responding to joint attention behaviors were examined as well as a solo attention (SA) control condition. Participants included adults with autism spectrum disorder (ASD) (n = 13), a mean age‐ and sex‐matched neurotypical group (n = 14), and a separate group of neurotypical adults (n = 22). Significant differences were found between groups within social‐cognitive brain regions, including dorsal medial prefrontal cortex (dMPFC) and right posterior superior temporal sulcus (pSTS), during the RJA as compared to SA conditions. Region‐of‐interest analyses revealed a lack of signal differentiation between joint attention and control conditions within left pSTS and dMPFC in individuals with ASD. Within the pSTS, this lack of differentiation was characterized by reduced activation during joint attention and relative hyper‐activation during SA. These findings suggest a possible failure of developmental neural specialization within the STS and dMPFC to joint attention in ASD. Hum Brain Mapp 34:2511–2523, 2013. © 2012 Wiley Periodicals, Inc.     

Auditory temporal envelope processing in a patient with left-hemisphere damage

Abstract

Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.     

Ventral simultanagnosia and prosopagnosia for unfamiliar faces due to a right posterior superior temporal sulcus and angular gyrus lesion

We report a patient with ventral simultanagnosia, prosopagnosia for “unfamiliar faces” (dorsal prosopagnosia), spatial agraphia, and constructional disorder, particularly on the left spatial side, due to a lesion in the right posterior superior and middle temporal gyri and angular gyrus. The patient showed impairment of fundamental visual and visuospatial recognition, such as in object size, configuration, and horizontal point location, which probably underlay the mechanism of simultanagnosia and prosopagnosia. This case also suggests that the coexistence of simultanagnosia and prosopagnosia results from a right hemispheric insult, and damage to the temporoparietal area interrupts the incorporation of spatial information into object recognition. This disconnection of information flow, together with impaired object recognition per se, may impair the parallel processing of multiple objects, leading to object-by-object or part-by-part recognition.     

Evidence for a social function of the anterior temporal lobes: Low-frequency rTMS reduces implicit gender stereotypes

By nature, stereotypes require processes of categorization or semantic association, including social information about groups of people. There is empirical evidence that the anterior temporal lobe (ATL) processes domain‐general semantic information, and supports social knowledge. A recent study showed that inhibitory repetitive transcranial magnetic stimulation (rTMS) to the ATL reduced racial stereotypes on an implicit association test (IAT). However, it was not determined whether this was caused by changes to specific social, or general semantic processing, or both. The current study addresses these theoretical issues. The design investigated the effect of rTMS to the left or right ATL, or a sham stimulation, on a social IAT (gender stereotypes), a non-social IAT (living versus non-living associations), and a non-semantic control (Stroop) task. The results showed that low-frequency rTMS to both left and right ATL significantly reduced D-scores on the gender IAT compared to the sham group; however, there were no differences on the non-social IAT or the Stroop. The findings show the ATL has a role in mediating stereotypes, and the decrease of bias after stimulation could be due to weakening of social stereotypical associations either within the ATL or via a network of brain regions connected with the ATL.