Object Size Information Research Articles

Action prediction in psychosis

Aberrant motor-sensory predictive functions have been linked to symptoms of psychosis, particularly reduced attenuation of self-generated sensations and misattribution of self-generated actions. Building on the parallels between prediction of self- and other-generated actions, this study aims to investigate whether individuals with psychosis also demonstrate abnormal perceptions and predictions of others’ actions. Patients with psychosis and matched controls completed a two-alternative object size discrimination task. In each trial, they observed reaching actions towards a small and a large object, with varying levels of temporal occlusion ranging from 10% to 80% of movement duration. Their task was to predict the size of the object that would be grasped. We employed a novel analytic approach to examine how object size information was encoded and read out across progressive levels of occlusion with single-trial resolution. Patients with psychosis exhibited an overall pattern of reduced and discontinuous evidence integration relative to controls, characterized by a period of null integration up to 20% of movement duration, during which they did not read any size information. Surprisingly, this drop in accuracy in the initial integration period was not accompanied by a reduction in confidence. Difficulties in action prediction were correlated with the severity of negative symptoms and impaired functioning in social relationships.

Deep ugrizY imaging and DEEP2/3 spectroscopy: a photometric redshift testbed for LSST and public release of data from the DEEP3 Galaxy Redshift Survey

ABSTRACT We present catalogues of calibrated photometry and spectroscopic redshifts in the Extended Groth Strip, intended for studies of photometric redshifts (photo-z’s). The data includes ugriz photometry from Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) and Y-band photometry from the Subaru Suprime camera, as well as spectroscopic redshifts from the DEEP2, DEEP3, and 3D-HST surveys. These catalogues incorporate corrections to produce effectively matched-aperture photometry across all bands, based upon object size information available in the catalogue and Moffat profile point spread function fits. We test this catalogue with a simple machine learning-based photometric redshift algorithm based upon Random Forest regression, and find that the corrected aperture photometry leads to significant improvement in photo-z accuracy compared to the original SExtractor catalogues from CFHTLS and Subaru. The deep ugrizY photometry and spectroscopic redshifts are well suited for empirical tests of photometric redshift algorithms for LSST. The resulting catalogues are publicly available at http://d-scholarship.pitt.edu/36064/. We include a basic summary of the strategy of the DEEP3 Galaxy Redshift Survey to accompany the recent public release of DEEP3 data.

Real-world size coding of solid objects, but not 2-D or 3-D images, in visual agnosia patients with bilateral ventral lesions

Patients with visual agnosia show severe deficits in recognizing two-dimensional (2-D) images of objects, despite the fact that early visual processes such as figure-ground segmentation, and stereopsis, are largely intact. Strikingly, however, these patients can nevertheless show a preservation in their ability to recognize real-world objects –a phenomenon known as the ‘real-object advantage’ (ROA) in agnosia. To uncover the mechanisms that support the ROA, patients were asked to identify objects whose size was congruent or incongruent with typical real-world size, presented in different display formats (real objects, 2-D and 3-D images). While recognition of images was extremely poor, real object recognition was surprisingly preserved, but only when physical size matched real-world size. Analogous display format and size manipulations did not influence the recognition of common geometric shapes that lacked real-world size associations. These neuropsychological data provide evidence for a surprising preservation of size-coding of real-world-sized tangible objects in patients for whom ventral contributions to image processing are severely disrupted. We propose that object size information is largely mediated by dorsal visual cortex and that this information, together with detailed representation of object shape which is also subserved by dorsal cortex, serve as the basis of the ROA.

Decreased attention to object size information in scale errors performers

Young children sometimes make serious attempts to perform impossible actions on miniature objects as if they were full-size objects. The existing explanations of these curious action errors assume (but never explicitly tested) children's decreased attention to object size information. This study investigated the attention to object size information in scale errors performers. Two groups of children aged 18–25 months (N=52) and 48–60 months (N=23) were tested in two consecutive tasks: an action task that replicated the original scale errors elicitation situation, and a looking task that involved watching on a computer screen actions performed with adequate to inadequate size object. Our key finding – that children performing scale errors in the action task subsequently pay less attention to size changes than non-scale errors performers in the looking task – suggests that the origins of scale errors in childhood operate already at the perceptual level, and not at the action level.

Grasping a 2D object: terminal haptic feedback supports an absolute visuo-haptic calibration.

Grasping a three-dimensional (3D) object results in the specification of motor output via absolute size information. In contrast, the impoverished visual cues (e.g., binocular and vergence) associated with grasping a two-dimensional (2D) object are reported to render aperture formation via an object's perceptual and relative visual features. It is, however, important to recognize that 3D and 2D grasping differ not only in terms of their visual properties, but also because the latter does not entail the provision of haptic feedback. As such, the present work examined whether haptic feedback influences the nature of the information supporting 2D grasping. Participants grasped differently sized 3D objects (i.e., 3D task) and completed a 'traditional' 2D grasping task to line drawings without receiving haptic feedback (i.e., 2DH- task). As well, we included a separate condition using the same objects as the 2DH- task; however, the experimenter placed a 3D object (i.e., one corresponding to the size of the 2D object) between the thumb and forefinger of participants' grasping limb once they completed their response (i.e., 2DH+ task). Thus, the 2DH+ task provided haptic feedback related to absolute object size. Notably, we computed just-noticeable-difference (JND) scores to determine whether the different tasks adhered to, or violated, the relative psychophysical principles of Weber's law. JNDs for the 2DH- task adhered to Weber's law, whereas 3D and 2DH+ tasks violated the law. Thus, results evince that 2DH- and 2DH+ tasks are specified via relative and absolute object size information, respectively. Accordingly, we propose that haptic feedback supports an absolute visuo-haptic calibration and contend that our results highlight the importance of multi-sensory cue integration in goal-directed grasping.

P174. Effects of left and right brain damage on anticipatory motor behavior during grasping and lifting with the ipsilesional hand

Behavioral studies in patients with left and right brain damage revealed the specialized function of both hemispheres in motor control. Recently, we investigated anticipatory grip force control in patients with stroke affecting the left or the right hemisphere during object lifting with the ipsilesional non-paretic hand. We found imprecise anticipation of grip force to the weight of everyday objects (like a carton with milk or a package of paper tissues) in patients with left brain damage while patients with right brain damage performed closer to normal. This finding suggests a particular role of the motor-dominant left brain in predicting object properties based on knowledge about the object identity. By contrast, we found no deficit of anticipatory grip force control in stroke patients when the initial weight information was provided by the size of the object. Also the perceptual size-weight-illusion was the same in patients and control subject. In the present study we tested material as the critical variable determining object weight. We hypothesized that the anticipation of material information as well as the so-called material-weight illusion may be reduced in patients with left brain damage, as material information about object characteristics may be a less direct cue to weight compared to size. Twelve patients with left brain damage (LBD), ten patients with right brain damage (RBD) and fourteen control subjects (CTR) lifted two pairs of identically-weighted objects which differed in size in the size-weight-illusion paradigm and in apparent material (polystyrene and aluminum) in the material-weight-illusion paradigm. In an additional control pair, the size and weight of two wooden blocks differed in the natural way. Participants’ grip forces and the lift forces were measured with a sensor (170 g) attached to the objects’ top surfaces. Subjects had to indicate which object in a pair is felt heavier before and after 6 lifts of each cube in a pair. Participants of all three groups experienced the size–weight–illusion. The material–weight–illusion was perceived less clearly without a clear difference between patients and control subjects. During the first lift of each object, the steepness of the grip force increase (quantified as the peak grip force rate) reflected the objects’ apparent weight as indicated by size. However variability was substantial in both patients groups. Different materials induced less clear differences in grip force rate. In particular, patients with left brain damage failed to scale their grip force profile according to the material. Also for the wooden object pair, data of LBD patients revealed a weaker anticipation of object properties than observed in the other groups. Our results confirm the normal processing of object size information for the scaling of grip forces and for the perception of the size-weight illusion in patients with brain damage, indicating that size processing is resistant to a wide range of brain damage. LBD patients in particular showed no consistent scaling of grip forces according to variations in material properties. Performance variability was however large in patients, suggesting that deficits depend on the specific lesion pattern which varied a lot across patients. In conclusion, the motor-dominant left hemisphere seems to play a prominent role in the processing of material information for object manipulation. However the responsibility seems to be less selective than when information is derived from object identity.