Recognition invariance obtained by extended and invariant features.

In performing recognition, the visual system shows a remarkable capacity to distinguish between significant and immaterial image changes, to learn from examples to recognize new classes of objects, and to generalize from known to novel objects. Here we focus on one aspect of this problem, the ability to recognize novel objects from different viewing directions. This problem of view-invariant recognition is difficult because the image of an object seen from a novel viewing direction can be substantially different from all previously seen images of the same object. We describe an approach to view-invariant recognition that uses extended features to generalize across changes in viewing directions. Extended features are equivalence classes of informative image fragments, which represent object parts under different viewing conditions. This representation is extracted during learning from images of moving objects, and it allows the visual system to generalize from a single view of a novel object, and to compensate for large changes in the viewing direction, without using three-dimensional information. We describe the model, its implementation and performance on natural face images, compare it to alternative approaches, discuss its biological plausibility, and its extension to other aspects of visual recognition. The results of the study suggest that the capacity of the recognition system to generalize to novel conditions in an efficient and flexible manner depends on the ongoing extraction of different families of informative features, acquired for different tasks and different object classes.     

Neural adaptation for novel objects during dynamic articulation

Human observers readily identify objects with moving parts, and recognize their underlying structure even when the component parts undergo complex movement. This suggests the existence of neural representations that are invariant to motion and state of articulation, which together allow our visual system to maintain ‘object constancy’. Ventral temporal cortex has previously been implicated in object perception and in coding object identity, but it is unclear where this is achieved when objects undergo motion-driven shape changes. In the present study, we use fMRI adaptation to probe the neural response properties when subjects view dynamic novel objects. Our results reveal neural selectivity for novel objects in the LOC region of the occipito-temporal lobe, even when those objects are viewed as moving and articulating. We also identify a bilateral area of posterior fusiform outside of the LOC with neural populations invariant to changes in the articulatory state of an object, a critical feature of object constancy. These results demonstrate the functional importance of ventral temporal cortex in the perception of moving objects, and the existence of neural populations coding for object constancy across movement and articulation.     

Object Recognition in the Cerebral Hemispheres as Revealed by Visual Field Experiments

Visual object recognition contains several stages of information processing carried out along the ventral visual pathway. Brain imaging and behavioural studies have suggested hemispheric asymmetries in object recognition, but the results do not provide a coherent view about the direction of the asymmetries or about the processing stage at which the asymmetries emerge. In order to clarify the contribution of the hemispheres to object recognition, two visual field experiments using normal participants were conducted. Experiment 1 used five different decision-making tasks to study processing at different stages of object recognition. The results showed that familiar objects were recognised faster when presented to the left visual field (LVF) than to the right visual field (RVF) in tasks requiring decisions between familiar objects vs scrambled objects or between familiar objects vs coherent novel objects, suggesting that the right hemisphere is superior in matching visual stimuli to stored representations. Experiment 2 replicated the LVF advantage in object decisions with the novel objects from Experiment 1 that had an unfamiliar overall shape but basic features similar to those of familiar objects. In addition, a RVF advantage emerged with chimeric objects composed by changing parts of familiar objects. The results suggest that the right hemisphere is superior at accessing the overall shape of objects from memory whereas the left hemisphere is superior at analysing whether the parts of objects match to memory representations.     

Hierarchical processing of face viewpoint in human visual cortex

The ability to recognize objects across different viewpoints (view invariance) is a remarkable property of the primate visual system. According to a prominent theory, view information is represented by view-selective mechanisms at early stages of visual processing and gradually becomes view invariant in high-level visual areas. Single-cell recording studies have also reported an intermediate step of partial view invariance for mirror-symmetric face views. Nevertheless, similar evidence for this type of hierarchical processing for face view has not been reported yet in the human visual cortex. The present functional magnetic resonance imaging study used state-of-the-art multivariate pattern analysis to explore face-view tuning in the human visual cortex. Our results revealed that consistent with a view-selective representation, face view can be successfully decoded in face and object-selective regions as well as in early visual cortex. Critically, similar neural representations for mirror-symmetric views were found in high-level but not in low-level visual areas. Our results support the notion of gradual emergence of view-invariant representation with invariance for mirror-symmetric images as an intermediate step and propose putative neural correlates of mirror-image confusion in the human brain.     

Spike Train Coactivity Encodes Learned Natural Stimulus Invariances in Songbird Auditory Cortex

The capacity for sensory systems to encode relevant information that is invariant to many stimulus changes is central to normal, real-world, cognitive function. This invariance is thought to be reflected in the complex spatiotemporal activity patterns of neural populations, but our understanding of population-level representational invariance remains coarse. Applied topology is a promising tool to discover invariant structure in large datasets. Here, we use topological techniques to characterize and compare the spatiotemporal pattern of coactive spiking within populations of simultaneously recorded neurons in the secondary auditory region caudal medial neostriatum of European starlings (Sturnus vulgaris). We show that the pattern of population spike train coactivity carries stimulus-specific structure that is not reducible to that of individual neurons. We then introduce a topology-based similarity measure for population coactivity that is sensitive to invariant stimulus structure and show that this measure captures invariant neural representations tied to the learned relationships between natural vocalizations. This demonstrates one mechanism whereby emergent stimulus properties can be encoded in population activity, and shows the potential of applied topology for understanding invariant representations in neural populations.SIGNIFICANCE STATEMENT Information in neural populations is carried by the temporal patterns of spikes. We applied novel mathematical tools from the field of algebraic topology to quantify the structure of these temporal patterns. We found that, in a secondary auditory region of a songbird, these patterns reflected invariant information about a learned stimulus relationship. These results demonstrate that topology provides a novel approach for characterizing neural responses that is sensitive to invariant relationships that are critical for the perception of natural stimuli.     

View‐invariant object recognition ability develops after discrimination,not mere exposure,at several viewing angles

One usually fails to recognize an unfamiliar object across changes in viewing angle when it has to be discriminated from similar distractor objects. Previous work has demonstrated that after long‐term experience in discriminating among a set of objects seen from the same viewing angle, immediate recognition of the objects across 30–60° changes in viewing angle becomes possible. The capability for view‐invariant object recognition should develop during the within‐viewing‐angle discrimination, which includes two kinds of experience: seeing individual views and discriminating among the objects. The aim of the present study was to determine the relative contribution of each factor to the development of view‐invariant object recognition capability. Monkeys were first extensively trained in a task that required view‐invariant object recognition (Object task) with several sets of objects. The animals were then exposed to a new set of objects over 26 days in one of two preparatory tasks: one in which each object view was seen individually, and a second that required discrimination among the objects at each of four viewing angles. After the preparatory period, we measured the monkeys’ ability to recognize the objects across changes in viewing angle, by introducing the object set to the Object task. Results indicated significant view‐invariant recognition after the second but not first preparatory task. These results suggest that discrimination of objects from distractors at each of several viewing angles is required for the development of view‐invariant recognition of the objects when the distractors are similar to the objects.     

Timecourse of object-related neural activity in the primate prefrontal cortex during a short-term memory task

We studied the timecourse of neural activity in the primate (Macacca mulatta) prefrontal (PF) cortex during an object delayed-matching-to-sample (DMS) task. To assess the effects of experience on this timecourse, we conducted the task using both novel and highly familiar objects. In addition, noise patterns containing no task-relevant information were used as samples on some trials. Comparison of average PF ensemble activity relative to baseline activity generated by objects and noise patterns revealed three distinct activity periods. (i) Sample onset elicited a transient sensory visual response. In this sensory period, novel objects elicited stronger average ensemble activity than both familiar objects and noise patterns. (ii) An intermediate period of elevated activity followed, which began before sample offset, and continued well into the delay period. In the intermediate period, activity was elevated for noise patterns and novel objects, but near baseline for familiar objects. (iii) Finally, after average ensemble activity reached baseline activity at the end of the intermediate period, a reactivation period occurred late in the delay. Experience had little effect during reactivation, where activity was elevated for both novel and familiar objects compared to noise patterns. We show that the ensemble average resembles the activity timecourse of many single prefrontal neurons. These results suggest that PF delay activity does not merely maintain recent sensory input, but is subject to more complex experience-dependent dynamics. This has implications for how delay activity is generated and maintained.     

How does the brain rapidly learn and reorganize view-invariant and position-invariant object representations in the inferotemporal cortex?

All primates depend for their survival on being able to rapidly learn about and recognize objects. Objects may be visually detected at multiple positions, sizes, and viewpoints. How does the brain rapidly learn and recognize objects while scanning a scene with eye movements, without causing a combinatorial explosion in the number of cells that are needed? How does the brain avoid the problem of erroneously classifying parts of different objects together at the same or different positions in a visual scene? In monkeys and humans, a key area for such invariant object category learning and recognition is the inferotemporal cortex (IT). A neural model is proposed to explain how spatial and object attention coordinate the ability of IT to learn invariant category representations of objects that are seen at multiple positions, sizes, and viewpoints. The model clarifies how interactions within a hierarchy of processing stages in the visual brain accomplish this. These stages include the retina, lateral geniculate nucleus, and cortical areas V1, V2, V4, and IT in the brain’s What cortical stream, as they interact with spatial attention processes within the parietal cortex of the Where cortical stream. The model builds upon the ARTSCAN model, which proposed how view-invariant object representations are generated. The positional ARTSCAN (pARTSCAN) model proposes how the following additional processes in the What cortical processing stream also enable position-invariant object representations to be learned: IT cells with persistent activity, and a combination of normalizing object category competition and a view-to-object learning law which together ensure that unambiguous views have a larger effect on object recognition than ambiguous views. The model explains how such invariant learning can be fooled when monkeys, or other primates, are presented with an object that is swapped with another object during eye movements to foveate the original object. The swapping procedure is predicted to prevent the reset of spatial attention, which would otherwise keep the representations of multiple objects from being combined by learning. Li and DiCarlo (2008) have presented neurophysiological data from monkeys showing how unsupervised natural experience in a target swapping experiment can rapidly alter object representations in IT. The model quantitatively simulates the swapping data by showing how the swapping procedure fools the spatial attention mechanism. More generally, the model provides a unifying framework, and testable predictions in both monkeys and humans, for understanding object learning data using neurophysiological methods in monkeys, and spatial attention, episodic learning, and memory retrieval data using functional imaging methods in humans.     

Successful episodic memory retrieval of newly learned faces activates a left fronto-parietal network

It is easier to recognize a familiar face than a newly learned face. The neural basis of familiar face recognition has been elucidated in functional imaging and lesion studies. Behavioural and neuropsychological data indicate, however, that brain systems involved in episodic retrieval of familiar and newly learned faces are distinct. In our study, 12 subjects viewed 30 novel faces in an encoding session. In the study condition, event-related functional magnetic resonance imaging (fMRI) was used to compare brain activation during correct recognition of the recently learned faces to that observed during correct rejection of unknown control faces. Differences were present in the left inferior parietal (BA 40) and left medial frontal/anterior cingulate (BA 32/9) cortex. These two regions may be part of a pathway in the dorsal visual stream, responsible for a "feeling of familiarity" in contrast to the ventral pathway in the temporal lobes, which is mainly involved in the recognition of personal identity.     

The pharmacology, neuroanatomy and neurogenetics of one-trial object recognition in rodents

Rats and mice are attracted by novel objects. They readily approach novel objects and explore them with their vibrissae, nose and forepaws. It is assumed that such a single explorative episode leaves a lasting and complex memory trace, which includes information about the features of the object explored, as well as where and even when the object was encountered. Indeed, it has been shown that rodents are able to discriminate a novel from a familiar object (one-trial object recognition), can detect a mismatch between the past and present location of a familiar object (one-trial object-place recognition), and can discriminate different objects in terms of their relative recency (temporal order memory), i.e., which one of two objects has been encountered earlier. Since the novelty-preference paradigm is very versatile and has some advantages compared to several other memory tasks, such as the water maze, it has become a powerful tool in current neurophamacological, neuroanatomical and neurogenetical memory research using both rats and mice. This review is intended to provide a comprehensive summary on key findings delineating the brain structures, neurotransmitters, molecular mechanisms and genes involved in encoding, consolidation, storage and retrieval of different forms of one-trial object memory in rats and mice.     

Superior voice recognition in a patient with acquired prosopagnosia and object agnosia

Anecdotally, it has been reported that individuals with acquired prosopagnosia compensate for their inability to recognize faces by using other person identity cues such as hair, gait or the voice. Are they therefore superior at the use of non-face cues, specifically voices, to person identity? Here, we empirically measure person and object identity recognition in a patient with acquired prosopagnosia and object agnosia. We quantify person identity (face and voice) and object identity (car and horn) recognition for visual, auditory, and bimodal (visual and auditory) stimuli. The patient is unable to recognize faces or cars, consistent with his prosopagnosia and object agnosia, respectively. He is perfectly able to recognize people's voices and car horns and bimodal stimuli. These data show a reverse shift in the typical weighting of visual over auditory information for audiovisual stimuli in a compromised visual recognition system. Moreover, the patient shows selectively superior voice recognition compared to the controls revealing that two different stimulus domains, persons and objects, may not be equally affected by sensory adaptation effects. This also implies that person and object identity recognition are processed in separate pathways. These data demonstrate that an individual with acquired prosopagnosia and object agnosia can compensate for the visual impairment and become quite skilled at using spared aspects of sensory processing. In the case of acquired prosopagnosia it is advantageous to develop a superior use of voices for person identity recognition in everyday life.     

Prosopagnosia and object agnosia without covert recognition

Investigations of the visual recognition abilities of the patient M.S. are reported. M.S. is unable to achieve overt recognition of any familiar faces, and many everyday objects. In Task 1 he showed semantic priming from name primes but not from face primes in a name recognition task. In Task 2 he showed no advantage in learning true (face + correct name) rather than untrue (face + someone else's name) pairings of faces and names. In Task 3 semantic priming of lexical decision was only found for object picture primes that M.S. was able to recognize overtly. In Task 4 faster matching of photographs of familiar than unfamiliar objects was only found for objects that M.S. was able to recognize overtly. These findings demonstrate an absence of covert recognition effects for M.S., consistent with the view that his impairment is primarily "perceptual" in nature.     

The long-term retention of events in monkey memory

Nine monkeys (Macaca fascicularis) demonstrated long-term memory for objects in a recognition task based on the non-matching-to-sample (NMTS) paradigm. In this task, the subjects were required to choose a novel object when it was paired with an alternative that had become familiar in previous NMTS training. When the familiar objects had been experienced an average of 3.4 times 4-9 months previously, 5 monkeys made 79% correct choices of the novel object. Three other monkeys exposed to the objects a mean of 12.8 times were 65% accurate at retention intervals of 20 months. A ninth subject achieved an accuracy of 68% after a retention interval of 34 months based on an exposure frequency of 10.6. These levels of performance indicate that in monkey event memory the mnemonic representation of an object is quite durable and a proportion of visual information may last for at least 3 years.     

Perceptual inference

Perceptual inference refers to the ability to infer sensory stimuli from predictions that result from internal neural representations built through prior experience. Methods of Bayesian statistical inference and decision theory model cognition adequately by using error sensing either in guiding action or in “generative” models that predict the sensory information. In this framework, perception can be seen as a process qualitatively distinct from sensation, a process of information evaluation using previously acquired and stored representations (memories) that is guided by sensory feedback. The stored representations can be utilised as internal models of sensory stimuli enabling long term associations, for example in operant conditioning. Evidence for perceptual inference is contributed by such phenomena as the cortical co-localisation of object perception with object memory, the response invariance in the responses of some neurons to variations in the stimulus, as well as from situations in which perception can be dissociated from sensation. In the context of perceptual inference, sensory areas of the cerebral cortex that have been facilitated by a priming signal may be regarded as comparators in a closed feedback loop, similar to the better known motor reflexes in the sensorimotor system. The adult cerebral cortex can be regarded as similar to a servomechanism, in using sensory feedback to correct internal models, producing predictions of the outside world on the basis of past experience.     

Biasing perception by spatial long-term memory

Human perception is highly flexible and adaptive. Selective processing is tuned dynamically according to current task goals and expectations to optimize behavior. Arguably, the major source of our expectations about events yet to unfold is our past experience; however, the ability of long-term memories to bias early perceptual analysis has remained untested. We used a noninvasive method with high temporal resolution to record neural activity while human participants detected visual targets that appeared at remembered versus novel locations within naturalistic visual scenes. Upon viewing a familiar scene, spatial memories changed oscillatory brain activity in anticipation of the target location. Memory also enhanced neural activity during early stages of visual analysis of the target and improved behavioral performance. Both measures correlated with subsequent target-detection performance. We therefore demonstrated that memory can directly enhance perceptual functions in the human brain.     

Finding and Not Finding Rat Perirhinal Neuronal Responses to Novelty

There is much evidence that the perirhinal cortex of both rats and monkeys is important for judging the relative familiarity of visual stimuli. In monkeys many studies have found that a proportion of perirhinal neurons respond more to novel than familiar stimuli. There are fewer studies of perirhinal neuronal responses in rats, and those studies based on exploration of objects, have raised into question the encoding of stimulus familiarity by rat perirhinal neurons. For this reason, recordings of single neuronal activity were made from the perirhinal cortex of rats so as to compare responsiveness to novel and familiar stimuli in two different behavioral situations. The first situation was based upon that used in “paired viewing” experiments that have established rat perirhinal differences in immediate early gene expression for novel and familiar visual stimuli displayed on computer monitors. The second situation was similar to that used in the spontaneous object recognition test that has been widely used to establish the involvement of rat perirhinal cortex in familiarity discrimination. In the first condition 30 (25%) of 120 perirhinal neurons were visually responsive; of these responsive neurons 19 (63%) responded significantly differently to novel and familiar stimuli. In the second condition eight (53%) of 15 perirhinal neurons changed activity significantly in the vicinity of objects (had “object fields”); however, for none (0%) of these was there a significant activity change related to the familiarity of an object, an incidence significantly lower than for the first condition. Possible reasons for the difference are discussed. It is argued that the failure to find recognition‐related neuronal responses while exploring objects is related to its detectability by the measures used, rather than the absence of all such signals in perirhinal cortex. Indeed, as shown by the results, such signals are found when a different methodology is used. © 2016 The Authors Hippocampus Published by Wiley Periodicals, Inc.     

False positives to confusable objects predict medial temporal lobe atrophy

Animal models agree that the perirhinal cortex plays a critical role in object recognition memory, but qualitative aspects of this mnemonic function are still debated. A recent model claims that the perirhinal cortex is required to recognize the novelty of confusable distractor stimuli, and that damage here results in an increased propensity to judge confusable novel objects as familiar (i.e., false positives). We tested this model in healthy participants and patients with varying degrees of perirhinal cortex damage, i.e., amnestic mild cognitive impairment and very early Alzheimer's disease (AD), with a recognition memory task with confusable and less confusable realistic object pictures, and from whom we acquired high‐resolution anatomic MRI scans. Logistic mixed‐model behavioral analyses revealed that both patient groups committed more false positives with confusable than less confusable distractors, whereas healthy participants performed comparably in both conditions. A voxel‐based morphometry analysis demonstrated that this effect was associated with atrophy of the anteromedial temporal lobe, including the perirhinal cortex. These findings suggest that also the human perirhinal cortex recognizes the novelty of confusable objects, consistent with its border position between the hierarchical visual object processing and medial temporal lobe memory systems, and explains why AD patients exhibit a heightened propensity to commit false positive responses with inherently confusable stimuli. © The Authors. Hippocampus Published by Wiley Periodicals, Inc.     

Apperceptive agnosia and face recognition

Abstract

Are faces and objects recognized by separate visual recognition systems or might a single system subserve the recognition of both classes of input? Recognition of faces and objects by a single system predicts that prosopagnosics, who selectively lose the ability to recognize faces due to brain damage, should also lose the ability to recognize objects. Contrary to this prediction, case studies of prosopagnosia have reported intact object recognition. Further support for separate visual recognition systems comes from the case of HH reported here. Following a stroke involving the left posterior cortex, HH has a severe apperceptive visual agnosia for visually presented objects and an alexia for words. Yet, he shows relatively spared visual face processing. Such a performance pattern completes a double dissociation between face and object processing when coupled with prosopaganosia. More importantly, HH is the first apperceptive visual object agnosic to demonstrate spared face processing. The severity of his object-processing deficit is such that from the earliest levels in the visual processing hierarchy, distinct neural substrates must be responsible for processing some objects and faces. These results are discussed as support for Farah's model (Visual agnosia: disorders of object recognition and what they tell us about normal vision. Cambridge, MA: MIT Press, 1990) of object, face and word recognition.     

Effects of gonadal hormones and persistent pain on non-spatial working memory in male and female rats

There are indications of a modulatory role carried out by gonadal hormones and pain in cognitive functions. We have examined this issue in male and female rats by assessing the impact of gonadectomy and persistent pain on the object recognition test. Intact and gonadectomized male and female rats were exposed to an open field (15 min) in which three objects were placed (Trial 1); the same test was repeated 2 h later (Trial 2), after the replacement of a "familiar" object with a novel one. Three days later (Day 2), the same procedure was repeated (Trial 3 and 4 with 2 h in between) but half of the animals were exposed to formalin-injection immediately before Trial 3. The latency, frequency and duration of approaching the three objects were recorded in each trial and compared by sex, gonadectomy and formalin treatment. The results showed that gonadectomized males and females had lower levels of approach to all objects and less locomotor/exploratory activity than intact animals in all experimental trials; their behaviour was not affected by repetition of the test or by pain. On Day 1, intact males showed a higher level of approach to the novel object than females. In intact males, the 2 h delay between the first and second trial failed to induce any significant modification of exploration of the novel object with respect to the familiar one, while in intact females the novel object was approached much less than the familiar one. Similarly on Day 2, the novel object was approached for a longer time by intact males than by all the other groups. In conclusion, our data show that physiological levels of circulating gonadal hormones significantly affected the performance of male but not female rats when exposed to the object recognition test.