Colour Terms Affect Detection of Colour and Colour-Associated Objects Suppressed from Visual Awareness

The idea that language can affect how we see the world continues to create controversy. A potentially important study in this field has shown that when an object is suppressed from visual awareness using continuous flash suppression (a form of binocular rivalry), detection of the object is differently affected by a preceding word prime depending on whether the prime matches or does not match the object. This may suggest that language can affect early stages of vision. We replicated this paradigm and further investigated whether colour terms likewise influence the detection of colours or colour-associated object images suppressed from visual awareness by continuous flash suppression. This method presents rapidly changing visual noise to one eye while the target stimulus is presented to the other. It has been shown to delay conscious perception of a target for up to several minutes. In Experiment 1 we presented greyscale photos of objects. They were either preceded by a congruent object label, an incongruent label, or white noise. Detection sensitivity (d’) and hit rates were significantly poorer for suppressed objects preceded by an incongruent label compared to a congruent label or noise. In Experiment 2, targets were coloured discs preceded by a colour term. Detection sensitivity was significantly worse for suppressed colour patches preceded by an incongruent colour term as compared to a congruent term or white noise. In Experiment 3 targets were suppressed greyscale object images preceded by an auditory presentation of a colour term. On congruent trials the colour term matched the object’s stereotypical colour and on incongruent trials the colour term mismatched. Detection sensitivity was significantly poorer on incongruent trials than congruent trials. Overall, these findings suggest that colour terms affect awareness of coloured stimuli and colour- associated objects, and provide new evidence for language-perception interaction in the brain.     

Size-Sensitive Perceptual Representations Underlie Visual and Haptic Object Recognition

A variety of similarities between visual and haptic object recognition suggests that the two modalities may share common representations. However, it is unclear whether such common representations preserve low-level perceptual features or whether transfer between vision and haptics is mediated by high-level, abstract representations. Two experiments used a sequential shape-matching task to examine the effects of size changes on unimodal and crossmodal visual and haptic object recognition. Participants felt or saw 3D plastic models of familiar objects. The two objects presented on a trial were either the same size or different sizes and were the same shape or different but similar shapes. Participants were told to ignore size changes and to match on shape alone. In Experiment 1, size changes on same-shape trials impaired performance similarly for both visual-to-visual and haptic-to-haptic shape matching. In Experiment 2, size changes impaired performance on both visual-to-haptic and haptic-to-visual shape matching and there was no interaction between the cost of size changes and direction of transfer. Together the unimodal and crossmodal matching results suggest that the same, size-specific perceptual representations underlie both visual and haptic object recognition, and indicate that crossmodal memory for objects must be at least partly based on common perceptual representations.     

Effects of olfactory stimuli on arm-reaching duration

The aim of the present study was to investigate the effects of olfactory stimuli on visually guided reaching. In Experiment 1, participants reached toward and grasped either a small (almond/strawberry) or a large (apple/orange) visual target. Any 1 of 4 odors corresponding to the visual stimuli or odorless air was administered before movement initiation. Within the same block of trials, participants smelled 1) an odor associated with an object of a different size than the target, 2) an odor associated with an object of a size equal to that of the target, or 3) odorless air. Results indicated that reaching duration was longer for trials in which the odor "size" and the visual target did not match than when they matched. In Experiment 2, the same procedures were applied but the "no-odor" trials were administered in a separate block to the "odor" trials. Similar results as for Experiment 1 were found. However, in contrast to Experiment 1, the presence of an odor increased the level of alertness resulting in a shortening of reaching duration. We contend that olfactory stimuli have the capacity to elicit motor plans interfering with those programmed for a movement toward a visual stimulus.     

Temporal brain dynamics of multiple object processing: the flexibility of individuation

The ability to process concurrently multiple visual objects is fundamental for a coherent perception of the world. A core component of this ability is the simultaneous individuation of multiple objects. Many studies have addressed the mechanism of object individuation but it remains unknown whether the visual system mandatorily individuates all relevant elements in the visual field, or whether object indexing depends on task demands. We used a neural measure of visual selection, the N2pc component, to evaluate the flexibility of multiple object individuation. In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present. While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory. However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.     

Dolphins Can Maintain Vigilant Behavior through Echolocation for 15 Days without Interruption or Cognitive Impairment

In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor visibility in the ocean, dolphins use echolocation to interrogate their environment. During echolocation, dolphin produce clicks and listen to returning echoes to determine the location and identity of objects. The extent to which individual dolphins are able to maintain continuous vigilance through this active sense is unknown. Here we show that dolphins may continuously echolocate and accurately report the presence of targets for at least 15 days without interruption. During a total of three sessions, each lasting five days, two dolphins maintained echolocation behaviors while successfully detecting and reporting targets. Overall performance was between 75 to 86% correct for one dolphin and 97 to 99% correct for a second dolphin. Both animals demonstrated diel patterns in echolocation behavior. A 15-day testing session with one dolphin resulted in near perfect performance with no significant decrement over time. Our results demonstrate that dolphins can continuously monitor their environment and maintain long-term vigilant behavior through echolocation.     

Visual exploration and object recognition by lattice deformation

Mechanisms of explicit object recognition are often difficult to investigate and require stimuli with controlled features whose expression can be manipulated in a precise quantitative fashion. Here, we developed a novel method (called "Dots"), for generating visual stimuli, which is based on the progressive deformation of a regular lattice of dots, driven by local contour information from images of objects. By applying progressively larger deformation to the lattice, the latter conveys progressively more information about the target object. Stimuli generated with the presented method enable a precise control of object-related information content while preserving low-level image statistics, globally, and affecting them only little, locally. We show that such stimuli are useful for investigating object recognition under a naturalistic setting--free visual exploration--enabling a clear dissociation between object detection and explicit recognition. Using the introduced stimuli, we show that top-down modulation induced by previous exposure to target objects can greatly influence perceptual decisions, lowering perceptual thresholds not only for object recognition but also for object detection (visual hysteresis). Visual hysteresis is target-specific, its expression and magnitude depending on the identity of individual objects. Relying on the particular features of dot stimuli and on eye-tracking measurements, we further demonstrate that top-down processes guide visual exploration, controlling how visual information is integrated by successive fixations. Prior knowledge about objects can guide saccades/fixations to sample locations that are supposed to be highly informative, even when the actual information is missing from those locations in the stimulus. The duration of individual fixations is modulated by the novelty and difficulty of the stimulus, likely reflecting cognitive demand.     

Dolphin sonar--modelling a new receiver concept

Observations suggest that dolphin sonars function well in the very shallow, reverberant, near-shore region of the ocean, and significantly out-perform man-made systems under such conditions. The echolocation characteristics of many small cetaceans have been measured directly and the high performance of biosonar systems is not in question, but explanations for their resolution, target detection, localization and tracking abilities are inadequate and deserve further investigation. The dolphin's lower jaw has been identified as part of an echo-receptor, and several hypotheses have been proposed to explain this. In one of these, the regularity of dolphin teeth was considered as a sonar array. This paper explores the physics of such systems with models based on established radar and sonar principles, and using data from various dolphin species. The insights gained from this modelling then lead to speculative proposals for new sonar receiver concepts that may have advantages over more conventional designs in shallow water operation.     

CETACEAN AUDITORY PSYCHOPHYSICS

ABSTRACT

The dolphin continues to capture the imagination of investigators because of its ability to echolocate. Echolocation is essentially a special extension and adaptation of the dolphin's hearing system, coupled with the animal's ability to generate special sounds. Humans have demonstrated the ability to judge room size based on reverberation from a voice, and some of the visually challenged use self-generated sounds to detect large reflective objects. Echolocation represents a highly refined acoustic ability on a broad acoustic sensory continuum. Research on the auditory and echolocation performance of cetaceans has moved forward slowly due to limited animal resources and the general high cost of maintaining these animals in a laboratory environment.

This paper reviews some of the more relevant psychoacoustic data on cetaceans, and concentrates on the bottlenose dolphin Tursiops truncatus. The information presented is not at all exhaustive. Early work with dolphins focused mainly on the animal's ability to use its echolocation system. Once echolocation capability was demonstrated using a blindfolded dolphin, the quest to understand dolphin sonar moved from qualifying the dolphin's echolocation skill to quantifying its basic capabilities.

Psychophysics, and more precisely psychoacoustics, provides the tools to study dolphin echolocation. The procedures, theories and even the apparatuses from the traditional psychoacoustics laboratory are adapted to the dolphin experimental setting to measure and analyze the sensory phenomenon of dolphin echolocation. Basic auditory phenomena such as the audiogram, the effects of masking, critical ratio and critical band, and interaural time and intensity discrimination capabilities have been explored in the dolphin. Additionally, special experiments investigating the psychoacoustics of the echolocation system in particular have been conducted.     

BEHAVIORAL EVIDENCE FOR HEARING THROUGH THE LOWER JAW BY AN ECHOLOCATING DOLPHIN (TURSIOPS TRUNCATUS)

On the basis of disputed physiological evidence the fat-filled lower jaw of odontocete cetaceans has previously been hypothesized as the primary pathway to the inner ear for acoustic signals. To gain behavioral evidence, a dolphin was trained to perform an echolocation task while wearing suction cups over its eyes and either of two neoprene robber hoods over its lower jaw. One hood allowed returning acoustic signals to pass. The other substantially attenuated such signals. The dolphin's performance was significantly hindered while wearing the attenuating hood ( P <. 001, ψ²) as would be expected if the lower jaw was critically important in the reception of high frequency signals.     

Field assessment of C‐POD performance in detecting echolocation click trains of bottlenose dolphins (Tursiops truncatus)

We evaluated the performance of dolphin echolocation detectors (C‐PODs) in the New River, North Carolina, by ground‐truthing echolocation detections with digital acoustic recordings. We deployed C‐PODs at three sites for a total of 204 monitoring hours. We also performed detection range trials at two sites where water depths ranged from 1.0 to 4.5 m. We used Detection Positive Minutes (DPMs), minutes of C‐POD recordings that contained at least one echolocation click train, to indicate the presence of at least one dolphin. The C‐PODs performed well in detecting dolphin click trains, although all units performed conservatively by failing to detect some echolocation events and therefore underestimated the true occurrence of dolphins. C‐PODs reported only a small number of false detections, as indicated by low false positive rates ranging between 1% and 4% for individual units. Overall, C‐PODs performed with a high accuracy (72%–91%) and detected echolocation at a distance of at least 933 m. We conclude that C‐PODs hold considerable promise in future monitoring studies of this species, but recommend a careful study design especially in complex, coastal environments.     

Hearing sensation levels of emitted biosonar clicks in an echolocating Atlantic bottlenose dolphin

Emitted biosonar clicks and auditory evoked potential (AEP) responses triggered by the clicks were synchronously recorded during echolocation in an Atlantic bottlenose dolphin (Tursiops truncatus) trained to wear suction-cup EEG electrodes and to detect targets by echolocation. Three targets with target strengths of -34, -28, and -22 dB were used at distances of 2 to 6.5 m for each target. The AEP responses were sorted according to the corresponding emitted click source levels in 5-dB bins and averaged within each bin to extract biosonar click-related AEPs from noise. The AEP amplitudes were measured peak-to-peak and plotted as a function of click source levels for each target type, distance, and target-present or target-absent condition. Hearing sensation levels of the biosonar clicks were evaluated by comparing the functions of the biosonar click-related AEP amplitude-versus-click source level to a function of external (in free field) click-related AEP amplitude-versus-click sound pressure level. The results indicated that the dolphin's hearing sensation levels to her own biosonar clicks were equal to that of external clicks with sound pressure levels 16 to 36 dB lower than the biosonar click source levels, varying with target type, distance, and condition. These data may be assumed to indicate that the bottlenose dolphin possesses effective protection mechanisms to isolate the self-produced intense biosonar beam from the animal's ears during echolocation.     

白鱀豚的声训练

1982年4月—1983年4月对一头白暨豚进行了训练,目标识别实验的结果表明,白暨豚愿意满足训练员的要求,且记忆力较强。     

Correlation model of object recognition by echolocating animals]

The model proposed in an attempt to find out physical bases of object perception during echolocation. It is shown that echolocational perception can be provided with correlational treatment of corresponding signals. The character of objects is determined by the comparison by echo probing accepted in the given cycle with typical distortions remembered in the course of individual experience of the animal. The distortions take place during the reflection of the probing impulse from these or those objects. "Binding" of the objects according to distance may be carried out by using the choice of typical distortions for corresponding correction of the copy of probing impulse, serving as a bearing signal of distance correlometer. The response of correlometer to the echo from correctly perceived target increases. The block-scheme of such correlation perception during echolocation is given. Performance of some experiments allowing to check and refine the model considered.     

Low-level correlations between object properties and viewpoint can cause viewpoint-dependent object recognition

Viewpoint-dependent recognition performance of 3-D objects has often been taken as an indication of a viewpoint-dependent object representation. This viewpoint dependence is most often found using metrically manipulated objects. We aim to investigate whether instead these results can be explained by viewpoint and object property (e.g. curvature) information not being processed independently at a lower level, prior to object recognition itself. Multidimensional signal detection theory offers a useful framework, allowing us to model this as a low-level correlation between the internal noise distributions of viewpoint and object property dimensions. In Experiment 1, we measured these correlations using both Yes/No and adjustment tasks. We found a good correspondence across tasks, but large individual differences. In Experiment 2, we compared these results to the viewpoint dependence of object recognition through a Yes/No categorization task. We found that viewpoint-independent object recognition could not be fully reached using our stimuli, and that the pattern of viewpoint dependence was strongly correlated with the low-level correlations we measured earlier. In part, however, the viewpoint was abstracted despite these correlations. We conclude that low-level correlations do exist prior to object recognition, and can offer an explanation for some viewpoint effects on the discrimination of metrically manipulated 3-D objects.     

Border collie comprehends object names as verbal referents

Four experiments investigated the ability of a border collie (Chaser) to acquire receptive language skills. Experiment 1 demonstrated that Chaser learned and retained, over a 3-year period of intensive training, the proper-noun names of 1022 objects. Experiment 2 presented random pair-wise combinations of three commands and three names, and demonstrated that she understood the separate meanings of proper-noun names and commands. Chaser understood that names refer to objects, independent of the behavior directed toward those objects. Experiment 3 demonstrated Chaser's ability to learn three common nouns - words that represent categories. Chaser demonstrated one-to-many (common noun) and many-to-one (multiple-name) name-object mappings. Experiment 4 demonstrated Chaser's ability to learn words by inferential reasoning by exclusion - inferring the name of an object based on its novelty among familiar objects that already had names. Together, these studies indicate that Chaser acquired referential understanding of nouns, an ability normally attributed to children, which included: (a) awareness that words may refer to objects, (b) awareness of verbal cues that map words upon the object referent, and (c) awareness that names may refer to unique objects or categories of objects, independent of the behaviors directed toward those objects.     

Neuropsychological studies of object recognition

It is well established that disorders of visual perception are associated with lesions in the right hemisphere. Performances on tasks as disparate as the identification of objects from unusual views of objects drawn so as to overlap, of fragmented letters, of familiar faces, and of anomalous features in drawings, have been shown to be impaired in patients with focal right posterior lesions. A series of investigations are reviewed, directed towards analysing the basis of these deficits. Explanations in terms of primary visual impairment can be rejected, as can an account in terms of faulty figure-ground organization. It is argued that a wide variety of such perceptual deficits--all of which are concerned with meaningful visual stimuli--can be encompassed by the notion of faulty perceptual categorization at an early post-sensory stage of object recognition. Moreover, there is evidence suggesting that some of these various perceptual deficits can be mutually dissociated. The concept of perceptual categorization is discussed in the wider context of tentative model of object recognition.     

A comparison of signal detection between an echolocating dolphin and an optimal receiver

Summary An electronic simulated target apparatus was used in a two-experiment study to compare the target detection performance of an echolocating bottlenose dolphin with an optimal receiver. Random Gaussian noise with a relatively flat spectrum from 20 to 160 kHz was used as a masking source. Experiment I was conducted to establish a technique for estimating the echo energy-to-noise ratio,E _e /N, at the dolphin's threshold of detection. Dolphins typically vary the amplitude of their emitted signal over a large range making it difficult to estimateE _e /N. In the first part of experiment I, the simulated echo was a double click, the pulses separated by 200 s, with each pulse being a replica of the dolphin's transmitted signal. A staircase psychophysical procedure was used to obtain the detection threshold, and the echo energy-to-noise ratio based on the highest amplitude click emitted per trial, (E _e /N)_max, was determined at each reversal point. The second echo type consisted of one of the animal's echolocation clicks, previously measured, digitized and stored in an erasable programmable read-only memory (EPROM). The electronic target simulator was modified so that every time the dolphin emitted an echolocation signal, the EPROM was triggered to produce two pulses separated by 200 s. On any trial, the EPROM signal was played back at a fixed amplitude, regardless of the amplitude of the dolphin's emitted signal. TheE _e /N obtained with the EPROM signal at threshold was found to be 2.9 dB lower than (E _e /N)_max obtained with the normal phantom target. Therefore an estimate ofE _e /N can be obtained by subtracting 2.9 dB from (E _e /N)_max.Experiment II was conducted to obtain isosensitivity data that could be plotted in an ROC (receiver operating characteristic) format. The response bias of the dolphin was manipulated by varying the food reinforcement payoff matrix. In terms of the ratio of correct detections to correct rejections, the payoff matrix was varied over four values: 11, 41, 81, and 14. A modified method of constants procedure was used to obtain the dolphin target detection performance data. Each session consisted of two 20-trial blocks in which a strong echo was used in the first block and a weak echo in the second block. The energy-to-noise ratio required by an optimal detector to approximate the dolphin's performance was obtained by determining the appropriate detection sensitivity,d, that best fitted the dolphin's data plotted in an ROC format. The results of experiment II indicated that the dolphin required approximately 7.4 dB higherE _e /N than an optimal detector to detect the phantom target.Abbreviations response bias - d detection sensitivity - E _e echo energy flux density - EPROM erasable programmable read-only memory - N noise spectral density - p(t) instantaneous acoustic pressure - P(Y/SN) probability of detection - P(Y/N) probability of false alarm - ROC receiver-operating-characteristics - SE source energy flux density     

Perceiving Object Shape from Specular Highlight Deformation,Boundary Contour Deformation,and Active Haptic Manipulation

It is well known that motion facilitates the visual perception of solid object shape, particularly when surface texture or other identifiable features (e.g., corners) are present. Conventional models of structure-from-motion require the presence of texture or identifiable object features in order to recover 3-D structure. Is the facilitation in 3-D shape perception similar in magnitude when surface texture is absent? On any given trial in the current experiments, participants were presented with a single randomly-selected solid object (bell pepper or randomly-shaped “glaven”) for 12 seconds and were required to indicate which of 12 (for bell peppers) or 8 (for glavens) simultaneously visible objects possessed the same shape. The initial single object’s shape was defined either by boundary contours alone (i.e., presented as a silhouette), specular highlights alone, specular highlights combined with boundary contours, or texture. In addition, there was a haptic condition: in this condition, the participants haptically explored with both hands (but could not see) the initial single object for 12 seconds; they then performed the same shape-matching task used in the visual conditions. For both the visual and haptic conditions, motion (rotation in depth or active object manipulation) was present in half of the trials and was not present for the remaining trials. The effect of motion was quantitatively similar for all of the visual and haptic conditions–e.g., the participants’ performance in Experiment 1 was 93.5 percent higher in the motion or active haptic manipulation conditions (when compared to the static conditions). The current results demonstrate that deforming specular highlights or boundary contours facilitate 3-D shape perception as much as the motion of objects that possess texture. The current results also indicate that the improvement with motion that occurs for haptics is similar in magnitude to that which occurs for vision.     

Associatieve visuele agnosie. De minder zichtbare gevolgen van een herseninfarct

After a cerebral infarction, some patients acutely demonstrate contralateral hemiplegia, or aphasia. Those are the obvious symptoms of a cerebral infarction. However, less visible but burdensome consequences may go unnoticed without closer investigation. The importance of a thorough clinical examination is exemplified by a single case study of a 72-year-old, right-handed male. Two years before he had suffered from an ischemic stroke in the territory of the left posterior cerebral artery, with right homonymous hemianopia and global alexia (i.e., impairment in letter recognition and profound impairment of reading) without agraphia. Naming was impaired on visual presentation (20%-39% correct), but improved significantly after tactile presentation (87% correct) or verbal definition (89%). Pre-semantic visual processing was normal (correct matching of different views of the same object), as was his access to structural knowledge from vision (he reliably distinguished real objects from non-objects). On a colour decision task he reliably indicated which of two items was coloured correctly. Though he was unable to mime how visually presented objects were used, he more reliably matched pictures of objects with pictures of a mime artist gesturing the use of the object. He obtained normal scores on word definition (WAIS-III), synonym judgment and word-picture matching tasks with perceptual and semantic distractors. He however failed when he had to match physically dissimilar specimens of the same object or when he had to decide which two of five objects were related associatively (Pyramids and Palm Trees Test). The patient thus showed a striking contrast in his intact ability to access knowledge of object shape or colour from vision and impaired functional and associative knowledge. As a result, he could not access a complete semantic representation, required for activating phonological representations to name visually presented objects. The pattern of impairments and preserved abilities is considered to be a specific difficulty to access a full semantic representation from an intact structural representation of visually presented objects, i.e., a form of visual object agnosia.     

Object familiarization and novel-object preference in rats

We investigated whether object familiarization was related to novel-object preference in the novel-object preference (NOP) test in rats. In Experiment 1, we found that no significant correlation existed between the time spent investigating 2 identical copies of a sample object and the degree of preference for a novel object. In Experiment 2, rats investigated 2 identical sample objects for a total of 5, 30, 60, 90 or 120 s. Investigatory preference for the novel object was compared to chance expectancy as well as between the groups. Only the 90-s group and the 120-s group displayed above-chance investigatory preference for the novel object, but novel-object preference for these 2 groups did not differ from each other, suggesting that a minimal amount of sample object investigation is necessary for rats to develop a novel-object preference, beyond which no increase in novel-object preference was found. In Experiments 3 and 4, normal rats and rats with hippocampal lesions were given repeated test trials, with the same sample object presented with a different novel object, at 24-h and (Experiment 3) and 35-s intervals (Experiment 4). In both experiments, novel-object preference did not increase in magnitude with repeated sample object exposures, suggesting that increased familiarity with the sample object does not result in increased novel-object preference. Rats with lesions of the dorsal hippocampus showed an unreliable investigatory preference for the novel object. These results are discussed in terms of the potential limitations of the NOP test as a tool for the assessment of object-recognition memory in rats.