Neuronal representation of object orientation

Interpreting the orientation of objects: A cross-disciplinary review

Is object orientation an inherent aspect of the shape of the object or is it represented separately and bound to the object shape in a similar way to other features, such as colour? This review brings together findings from neuropsychological studies of patients with agnosia for object orientation and experimental studies of object perception in healthy individuals that provide converging evidence of separate processing of object identity and orientation. Individuals with agnosia for object orientation, which typically results from damage to the right parietal lobe, can recognize objects presented in a range of orientations yet are unable to interpret or discriminate the objects' orientation. Healthy individuals tested with briefly presented objects demonstrate a similar dissociation: object identity is extracted rapidly in an orientation-invariant way, whereas processing the object's orientation is slower, requires attention and is influenced by the degree of departure from the canonical orientation. This asymmetry in processing can sometimes lead to incorrect bindings between the identity and orientation of objects presented in close temporal proximity. Overall, the available evidence indicates that object recognition is achieved in a largely orientation-invariant manner and that interpreting the object's orientation requires an additional step of mapping this orientation-invariant representation to a spatial reference frame.

From intermediate shape-centered representations to the perception of oriented shapes: response to commentaries

In this response paper, we start by addressing the main points made by the commentators on the target article's main theoretical conclusions: the existence and characteristics of the intermediate shape-centered representations (ISCRs) in the visual system, their emergence from edge detection mechanisms operating on different types of visual properties, and how they are eventually reunited in higher order frames of reference underlying conscious visual perception. We also address the much-commented issue of the possible neural mechanisms of the ISCRs. In the final section, we address more specific and general comments, questions, and suggestions which, albeit very interesting, were less directly focused on the main conclusions of the target paper.

Shape-centered representations of bounded regions of space mediate the perception of objects

We report the study of a woman who perceives 2D bounded regions of space ("shapes") defined by sharp edges of medium to high contrast as if they were rotated by 90, 180 degrees around their centre, mirrored across their own axes, or both. In contrast, her perception of 3D, strongly blurred or very low contrast shapes, and of stimuli emerging from a collection of shapes, is intact. This suggests that a stage in the process of constructing the conscious visual representation of a scene consists of representing mutually exclusive bounded regions extracted from the initial retinotopic space in "shape-centered" frames of reference. The selectivity of the disorder to shapes originally biased toward the parvocellular subcortical pathway, and the absence of any other type of error, additionally invite new hypotheses about the operations involved in computing these "intermediate shape-centered representations" and in mapping them onto higher frames for perception and action.

Temporo-parietal brain regions are involved in higher order object perception

Lesions to posterior temporo-parietal brain regions are associated with deficits in perception of global, hierarchical shapes, but also with impairments in the processing of objects presented under demanding viewing conditions. Evidence from neuroimaging studies and lesion patterns observed in patients with simultanagnosia and agnosia for object orientation suggest similar brain regions to be involved in perception of global shapes and processing of objects in atypical ('non-canonical') orientation. In a localizer experiment, we identified individual temporo-parietal brain areas involved in global shape perception and found significantly higher BOLD signals during the processing of non-canonical compared to canonical objects. In a multivariate approach, we demonstrated that posterior temporo-parietal brain areas show distinct voxel patterns for non-canonical and canonical objects and that voxel patterns of global shapes are more similar to those of objects in non-canonical compared to canonical viewing conditions. These results suggest that temporo-parietal brain areas are not only involved in global shape perception but might serve a more general mechanism of complex object perception. Our results challenge a strict attribution of object processing to the ventral visual stream by suggesting specific dorsal contributions in more demanding viewing conditions.

Neuropsychological Changes in Complex Regional Pain Syndrome (CRPS)

Complex Regional Pain Syndrome (CRPS) is a poorly understood chronic pain condition of multifactorial origin. CRPS involves sensory, motor, and autonomic symptoms primarily affecting one extremity. Patients can also present with neuropsychological changes such as reduced attention to the CRPS-affected extremity, reminiscent of hemispatial neglect, yet in the absence of any brain lesions. However, this "neglect-like" framework is not sufficient to characterise the range of higher cognitive functions that can be altered in CRPS. This comprehensive literature review synthesises evidence of neuropsychological changes in CRPS in the context of potential central mechanisms of the disorder. The affected neuropsychological functions constitute three distinct but not independent groups: distorted body representation, deficits in lateralised spatial cognition, and impairment of non-spatially-lateralised higher cognitive functions. We suggest that many of these symptoms appear to be consistent with a broader disruption to parietal function beyond merely what could be considered "neglect-like." Moreover, the extent of neuropsychological symptoms might be related to the clinical signs of CRPS, and rehabilitation methods that target the neuropsychological changes can improve clinical outcomes in CRPS and other chronic pain conditions. Based on the limitations and gaps in the reviewed literature, we provide several suggestions to improve further research on neuropsychological changes in chronic pain.

Supramodal agnosia for oblique mirror orientation in patients with periventricular leukomalacia

Periventricular leukomalacia (PVL) is characterized by focal necrosis at the level of the periventricular white matter, often observed in preterm infants. PVL is frequently associated with motor impairment and with visual deficits affecting primary stages of visual processes as well as higher visual cognitive abilities. Here we describe six PVL subjects, with normal verbal IQ, showing orientation perception deficits in both the haptic and visual domains. Subjects were asked to compare the orientation of two stimuli presented simultaneously or sequentially, using both a two alternative forced choice (2AFC) orientation-discrimination and a matching procedure. Visual stimuli were oriented gratings or bars or collinear short lines embedded within a random pattern. Haptic stimuli comprised two rotatable wooden sticks. PVL patients performed at chance in discriminating the oblique orientation, both for visual and haptic stimuli. Moreover when asked to reproduce the oblique orientation, they often oriented the stimulus along the symmetric mirror orientation. The deficit generalized to stimuli varying in many low level features, was invariant for spatiotopic object orientation, and also occurred for sequential presentations. The deficit was specific to oblique orientations, and not for horizontal or vertical stimuli. These findings show that PVL can affect a specific network involved with the supramodal perception of mirror symmetry orientation.

Objects influence the shape of remembered views: examining global and local aspects of boundary extension

Boundary extension is a constructive memory error for views of scenes in which viewx tendto be remembered as more spatially expansive than they appeared. In seven experiments xwe examinedwhether local differences in boundary extension within views might exist by presenting par ticipants ith overhead views of single, elongated objects or object pairs on textured ground surfaces i:n whichobjects were oriented either vertically or horizontally. Memory for views' spatial expanse xwas testedwith either a view-recognition test or a border-adjustment test in which participants could ad just thespatial expanse of a test view using the computer's mouse. The border-adjustment test was uused tossess local boundary extension (primarily); the view-recognition test was used to assess paparticipants'emories for the overall spatial expanse of views (ie global boundary extension). Across exexperiments,n the border-adjustment tests specifically, participants showed more spatial expanse along the obobject'songer axis, in some cases restricting the view along the object's shorter axis. In addition, the rerecognition-t data revealed greater boundary extension for views with vertically oriented objects than for x.iviewsth horizontally oriented objects. Taken together, the results suggest that objects in scene x iviews canfect both local and global aspects of memory for spatial expanse of scene views.

Components of action representations evoked when identifying manipulable objects

We examined the influence of holding planned hand actions in working memory on the time taken to visually identify objects with handles. Features of the hand actions and position of the object's handle were congruent or incongruent on two dimensions: alignment (left vs. right) and orientation (horizontal vs. vertical). When an object was depicted in an upright view, subjects were slower to name it when its handle was congruent with the planned hand actions on one dimension but incongruent on the other, relative to when the object handle and actions were congruent on both or neither dimension. This pattern is consistent with many other experiments demonstrating that a cost occurs when there is partial feature overlap between a planned action and a perceived target. An opposite pattern of results was obtained when the depicted object appeared in a 90° rotated view (e.g., a beer mug on its side), suggesting that the functional goal associated with the object (e.g., drinking from an upright beer mug) was taken into account during object perception and that this knowledge superseded the influence of the action afforded by the depicted view of the object. These results have implications for the relationship between object perception and action representations, and for the mechanisms that support the identification of rotated objects.

Agnosia for mirror stimuli: a new case report with a small parietal lesion

Only seven cases of agnosia for mirror stimuli have been reported, always with an extensive lesion. We report a new case of an agnosia for mirror stimuli due to a circumscribed lesion. An extensive battery of neuropsychological tests and a new experimental procedure to assess visual object mirror and orientation discrimination were assessed 10 days after the onset of clinical symptoms, and 5 years later. The performances of our patient were compared with those of four healthy control subjects matched for age. This test revealed an agnosia for mirror stimuli. Brain imaging showed a small right occipitoparietal hematoma, encompassing the extrastriate cortex adjoining the inferior parietal lobe. This new case suggests that: (i) agnosia for mirror stimuli can persist for 5 years after onset and (ii) the posterior part of the right intraparietal sulcus could be critical in the cognitive process of mirror stimuli discrimination.

Hierarchical processing in Balint's syndrome: a failure of flexible top-down attention

Patients with Balint’ s syndrome are typically impaired at perceiving multiple objects simultaneously, and at evaluating the relationship between multiple objects in a scene (simultanagnosia). These deficits may not only be observed in complex scenes, but also when local elements of individual objects must be integrated into a perceptual global whole. Thus, unlike normal observers, patients with simultanagnosia typically show a bias towards the local forms, even to the extent that they cannot identify the global stimuli. However, we have previously shown that global processing is still attainable in Balint patients in certain scenarios (e.g., when local elements are unfamiliar). This suggests that in addition to a possible perceptual deficit that favors the local elements in these patients, impaired attentional control may be at the core of their unique performance. To test this hypothesis we manipulated the perceptual saliency of the local and global elements in a compound letter task so that it included global-more-salient or local-more-salient displays. We show that a Balint patient was able to accurately identify both global and local targets as long as they were the salient aspect of the compound letter. However, substantial impairment was evident when either the global or local elements were the less salient aspect of the compound letter. We conclude that in Balint’ s syndrome there is a failure of flexible top-down attention both in biasing attention away from salient irrelevant aspects of the display (salience-based-selection) and in impaired disengagement from irrelevant but salient items once they have been selected.

Memory for objects in canonical and noncanonical viewpoints

This article investigates how the perspective from which we see an object affects memory. Object identification can be affected by the orientation of the object. Palmer, Rosch, and Chase (1981) coined the term canonical to describe perspectives in which identification performance is best. We present two experiments that tested the effects of object perspective on memory. Our results revealed a double dissociation between task (recognition and recall) and type of object perspective. In recognition, items studied in the noncanonical viewpoint produced higher proportions of "old" responses than did items studied in the canonical viewpoint, whereas new objects presented from a noncanonical viewpoint produced fewer "old" responses than did new objects presented from the canonical viewpoint. In free recall, conversely, objects studied from the noncanonical viewpoint produced lower recall rates than did objects studied from the canonical viewpoint. These results, which reveal a pattern similar to word frequency effects, support the psychological reality of canonical viewpoints and the frequency-of-exposure-based accounts of canonical viewpoint effects.

Effects of right parietal transcranial magnetic stimulation on object identification and orientation judgments

We investigated the role played by the right parietal lobe in object identification and the ability to interpret object orientation, using transcranial magnetic stimulation (TMS) to momentarily interfere with ongoing cortical activity. Short trains of TMS pulses (12 Hz) were applied to a site overlying the right intraparietal sulcus/inferior parietal lobe while subjects performed either object identification tasks (i.e., picture-word verification and categorizing objects as natural or manufactured) or object orientation judgment tasks (i.e., picture-arrow verification and deciding whether an object was rotated clockwise or counterclockwise). Across different tasks, right parietal TMS impaired orientation judgments, but facilitated object identification, compared to TMS applied to a brain vertex control site. These complementary findings demonstrate that the right parietal lobe--a region belonging to the dorsal visual stream--is critical for processing the spatial attributes of objects, but not their identity. The observed improvement in object recognition, however, suggests an indirect role for the right parietal lobe in object recognition. We propose that this involves the creation of a spatial reference frame for the object, which allows interaction with the object and the individuation of specific viewing instances.

Cognitive representation of orientation: a case study

Although object orientation in the human brain has been discussed extensively in the literature, the nature of the underlying cognitive representation(s) remains uncertain. We investigated orientation perception in BC, a patient with bilateral occipital and parietal damage from a herpes encephalitis infection. Our results show that in addition to general inaccuracy in discriminating and reproducing line orientations, her errors take the form of left-right mirror reflections across a vertical coordinate axis. We propose that in BC, the cognitive impairment is in failing to represent the direction of tilt for line orientations. Our results suggest that there exists a level of representation in the human brain at which line orientations are represented compositionally, such that the direction of a line orientation's tilt from a vertical mental reference meridian is coded independently of the magnitude of its angular displacement. Reflection errors across a vertical axis were observed both in visual and tactile line orientation tasks, demonstrating that these errors arise at a supra-modal level of representation not restricted to vision, or, alternatively, that visual-like representations are being constructed from the tactile input.

Repetition blindness is orientation blind

In identifying rapid sequences of three letters, subjects were worse at identifying the first and third letters when they were the same than when they were different, indicating repetition blindness (RB). This effect occurred regardless of the angular orientations of the letters, but was more pronounced when the orientations of the repeated letters were different than when they were the same. In a second experiment, RB was also evident when the first and third letters were lowercase bs or ds, presented upright or inverted, even though they are differently named when inverted (q and p, respectively). Conversely, a third experiment showed that RB occurred when the letters had the same names but were repeated in different case. These results suggest that the early extraction of letter shape is independent of its orientation and left-right sense, and that RB can occur at the levels of both shape and name.

Turning objects on their heads: The influence of the stored axis on object individuation

We used repetition blindness (RB) as a measure of object recognition and compared the pattern of RB obtained for objects with a well-established upright orientation (mono-oriented objects) and those without a usual upright orientation (polyoriented objects), when the critical objects were either in identical orientations or differed by 30 degrees, 60 degrees, 90 degrees, or 180 degrees. Overall, we found robust RB despite differences in orientation, consistent with the idea that object recognition, as indexed by RB, is largely independent of orientation. However, whereas for polyoriented objects RB was obtained in all orientation conditions, for mono-oriented objects there was no RB between upright and upside-down versions of the stimuli. These findings suggest that the usual orientation of an object-when it exists-is stored in memory and can facilitate orientation processing when the principal axis of a viewed object is aligned with the stored axis orientation. This, in turn, allows for more rapid and successful construction of distinct episodic representations of an object, thus alleviating RB.

Visual search for object orientation can be modulated by canonical orientation

The authors studied the influence of canonical orientation on visual search for object orientation. Displays consisted of pictures of animals whose axis of elongation was either vertical or tilted in their canonical orientation. Target orientation could be either congruent or incongruent with the object's canonical orientation. In Experiment 1, vertical canonical targets were detected faster when they were tilted (incongruent) than when they were vertical (congruent). This search asymmetry was reversed for tilted canonical targets. The effect of canonical orientation was partially preserved when objects were high-pass filtered, but it was eliminated when they were low-pass filtered, rendering them as unfamiliar shapes (Experiment 2). The effect of canonical orientation was also eliminated by inverting the objects (Experiment 3) and in a patient with visual agnosia (Experiment 4). These results indicate that orientation search with familiar objects can be modulated by canonical orientation, and they indicate a top-down influence on orientation processing.

Orientation-invariant object recognition: evidence from repetition blindness

The question of whether object recognition is orientation-invariant or orientation-dependent was investigated using a repetition blindness (RB) paradigm. In RB, the second occurrence of a repeated stimulus is less likely to be reported, compared to the occurrence of a different stimulus, if it occurs within a short time of the first presentation. This failure is usually interpreted as a difficulty in assigning two separate episodic tokens to the same visual type. Thus, RB can provide useful information about which representations are treated as the same by the visual system. Two experiments tested whether RB occurs for repeated objects that were either in identical orientations, or differed by 30, 60, 90, or 180 degrees . Significant RB was found for all orientation differences, consistent with the existence of orientation-invariant object representations. However, under some circumstances, RB was reduced or even eliminated when the repeated object was rotated by 180 degrees , suggesting easier individuation of the repeated objects in this case. A third experiment confirmed that the upside-down orientation is processed more easily than other rotated orientations. The results indicate that, although object identity can be determined independently of orientation, orientation plays an important role in establishing distinct episodic representations of a repeated object, thus enabling one to report them as separate events.

Similar cortical correlates underlie visual object identification and orientation judgment

Visual object perception has been suggested to follow two different routes in the human brain: a ventral, view-invariant occipital-temporal route processes object identity, whereas a dorsal, view-dependent occipital-parietal route processes spatial properties of an object. Using fMRI, we addressed the question whether these routes are exclusively involved in either object recognition or spatial representation. We presented subjects with images of natural objects and involved them either in object identification or object orientation judgment task. For both tasks, we observed activation in ventro-temporal as well as parietal areas bilaterally, with significantly stronger responses for the orientation judgment in both ventro-temporal as well as parietal areas. Our findings suggest that object identification and orientation judgment do not follow strictly separable cortical pathways, but rather involve both the dorsal and the ventral stream.

A 3-year follow-up study of 'orientation agnosia'

Dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients, but the long-term course of this deficit has not been reported so far. Here, we describe the case of a 32-year-old female who had bilateral occipito-temporal damage caused by a cerebrovascular accident. Neuropsychological assessment performed at 6 months after the occurrence of the cerebrovascular accident revealed that she was almost generally agnostic for object orientation. The patient was then re-tested 3 years later, when she showed apparently striking recovery in her ability to determine object orientation. However, closer examination revealed that she still displayed the same impairment, although at this time, it was only for objects presented in non-cardinal angles. Moreover, she had problems mostly discriminating orientations that differed by small amounts. The ability of patients to discriminate a variety of orientations should be further tested in future investigations in this field.

Selective rotation of egocentric spatial representation following right putaminal hemorrhage

Although the role of frontoparietal cortex in spatial egocentric processing is well established, recent animal-lesion and human functional imaging studies have suggested that the neostriatum may also be a critical modulator in the processing of body-centred spatial orientation. We describe here a patient with right putamen-centred hemorrhage who exhibited a consistent counterclockwise rotation of approximately 90 degrees when drawing and writing from memory. A more detailed assessment with a series of representational clock tests demonstrated that the rotation was present only in tasks requiring the use of egocentric cues. In the absence of external cues the patient would adopt and maintain a stable but incorrectly-oriented egocentric representation of the imagined or recollected object. By contrast, performance could be rectified by presentation of correctly-oriented stimuli. These findings suggest that the putamen is part of a circuit underlying egocentric, as opposed to allocentric, representation of space in humans.

Distributing vertical forces between the digits during gripping and lifting: the effects of rotating the hand versus rotating the object

During pinch grip we partition the vertical tangential forces at the digits according to the friction at the grip surfaces, and the mass distribution of the object. However, we cannot predictively partition the vertical forces to adjust to new frictional conditions after viewing a 180-deg rotation of an object with different textures at each grip surface. Hence, the processes that lead to predictive force partitioning may not access object representations, thereby suggesting that these processes are digit-specific. If this is true, then we should fail to predictively partition our fingertip forces when we rotate our hand. We tested this prediction by comparing the effects of object rotation with hand rotation for repeated lifts of an object that had one slippery grip surface and one rough grip surface. Subjects did not predictively redistribute the vertical tangential forces upon grasping the rotated object. Following object rotation, the vertical tangential force trajectories during the first 100 ms after contact indicated that 12/15 subjects failed to anticipate the reversed digit-friction relationships. All subjects appropriately partitioned the vertical tangential forces between the digits by the second lift after object rotation, confirming previous reports that sensory signals update the memory associated with lifting the object. In contrast, after hand rotation, 13/15 subjects anticipated the new digit-friction relationships and upon grasping the object immediately generated a steep rise in the vertical force trajectory at the rough surface. They also delayed the initial rise in vertical tangential force at the digit encountering the low-friction surface by approximately 65 ms. Thus, anticipatory partitioning of vertical fingertip forces is not strictly digit-specific. Internally driven motor plans can access the relevant memories or internal models for predictively partitioning the vertical tangential forces. It is not clear if this process involves rotating internal representations of fingertip force directly, or if the forces are derived after internally rotating a representation of the object. In contrast to the robust effects of vision on reach kinematics, or on wrist and finger configuration, visual signals about object rotation and orientation apparently do not influence vertical tangential fingertip forces.

A particular difficulty in discriminating between mirror images

We investigated the selective impairment of mirror image discrimination in a patient with bilateral parieto-occipital lesions (FIM). We report a difficulty with the discrimination between mirror images more selective than has been previously reported (Turnbull OH, McCarthy RA. Failure to discriminate between mirror-image objects: a case of viewpoint-independent object recognition? Neurocase 1996;2:63). FIM was asked to judge, in five same/different experiments, whether pairs of simultaneously presented line drawings of objects were identical. FIM demonstrated only a minor impairment in discriminating between orientations in the picture plane but was at chance in making discrimination between mirror images. An experiment with normal observers established that our results were not due to differences in task difficulty. Two further experiments investigated the effects of rotation on the discrimination of letters and geometric shapes. FIM's impairment extended to geometric shapes but not to letters. These results would be consistent with the preservation of an abstract representation for object recognition that did not code the difference between mirror image views.

Object orientation agnosia: a failure to find the axis?

A dissociation between the ability to recognize misoriented objects and to determine their orientation has been reported in a small number of patients with vascular lesions. In this article, we describe a 57-year-old man with probable Alzheimer' s disease who shows the same dissociation. Neuroimaging findings indicated marked hypometabolism in the posterior cortical regions, particularly the postero-superior parietal lobes. Clinically, the patient had good object recognition accompanied by severely impaired spatial abilities. The experimental investigations comprised a variety of tasks in which he identified misoriented objects, evaluated the orientation of single objects, or discriminated the orientation of simultaneously presented items. Results revealed that his object recognition was independent of orientation and was largely mediated by salient features. With respect to orientation judgements, the patient displayed a profound inability to judge the orientation of nonupright objects, but remarkably intact (though largely implicit) knowledge of the upright orientation. Strikingly, his orientation judgements were also more accurate for upside-down objects than for other orientations (i.e., 90 degrees ). We interpret these results as evidence that judgements about object orientation are facilitated when the orientation of the principal axis of the object matches that of an internal representation. We propose that the inability to determine other orientations may be due to the failure of an "axis-finding" mechanism implemented in the posterior parietal lobes, that translates between object-centered and eye-centered coordinates appropriate for guiding visual scanning.