Illusion susceptibility in domestic dogs

Domestic dogs play many vital roles in human lives; however, relatively little is known about how they perceive the world visually. Given dogs’ recent popularity as a subject in cognitive and behavioural studies, it is important to understand how they visually interpret the world around them. One way to evaluate perception is to assess illusion susceptibility; specifically, how visual information is processed, interpreted and modified post-retinally. While illusion susceptibility has been used across a variety of species to comparatively assess the similarities and differences in visual processing and perception, this relatively novel methodological approach has only recently been adapted to evaluate perception in domestic dogs. Here, we present a comprehensive overview of the findings from studies that have evaluated domestic dogs’ illusion susceptibility, highlighting the relevance of these results for those studying illusion susceptibility in animals as well as canine behaviour and cognition. More specifically, the ultimate goal of this review is to answer the questions: (a) Are dogs susceptible to visual illusions? (b) If so, are they susceptible to illusions in a way that parallels humans and/or other animals? (c) Are findings, within dogs, consistent and if not, how might these be interpreted and explained?     

综述: 初级视皮层的亮度信息加工

亮度(luminance)是最基本的视觉信息.与其他视觉特征相比,由于视神经元对亮度刺激的反应较弱,并且许多神经元对均匀亮度无反应,对亮度信息编码的神经机制知之甚少.初级视皮层部分神经元对亮度的反应要慢于对比度反应,被认为是由边界对比度诱导的亮度知觉(brightness)的神经基础.我们的研究表明,初级视皮层许多神经元的亮度反应要快于对比度反应,并且这些神经元偏好低的空间频率、高的时间频率和高的运动速度,提示皮层下具有低空间频率和高运动速度通路的信息输入对产生初级视皮层神经元的亮度反应有贡献.已经知道初级视皮层神经元对空间频率反应的时间过程是从低空间频率到高空间频率,我们发现的早期亮度反应是对极低空间频率的反应,与这一时间过程是一致的,是这一从粗到细的视觉信息加工过程的第一步,揭示了处理最早的粗的视觉信息的神经基础.另外,初级视皮层含有偏好亮度下降和高运动速度的神经元,这群神经元的活动有助于在光照差的环境中检测高速运动的低亮度物体.     

Changing the Chevreul illusion by a background luminance ramp: lateral inhibition fails at its traditional stronghold--a psychophysical refutation

The Chevreul illusion is a well-known 19^th century brightness illusion, comprising adjacent homogeneous grey bands of different luminance, which are perceived as inhomogeneous. It is generally explained by lateral inhibition, according to which brighter areas projected to the retina inhibit the sensitivity of neighbouring retinal areas. Lateral inhibition has been considered the foundation-stone of early vision for a century, upon which several computational models of brightness perception are built. One of the last strongholds of lateral inhibition is the Chevreul illusion, which is often illustrated even in current textbooks. Here we prove that lateral inhibition is insufficient to explain the Chevreul illusion. For this aim, we placed the Chevreul staircase in a luminance ramp background, which noticeably changed the illusion. In our psychophysical experiments, all 23 observers reported a strong illusion, when the direction of the ramp was identical to that of the staircase, and all reported homogeneous steps (no illusion) when its direction was the opposite. When the background of the staircase was uniform, 14 saw the illusion, and 9 saw no illusion. To see whether the change of the entire background area or that of the staircase boundary edges were more important, we placed another ramp around the staircase, whose direction was opposite to that of the original, larger ramp. The result is that though the inner ramp is rather narrow (mean = 0.51 deg, SD = 0.48 deg, N = 23), it still dominates perception. Since all conditions of the lateral inhibition account were untouched within the staircase, lateral inhibition fails to model these perceptual changes. Area ratios seem insignificant; the role of boundary edges seems crucial. We suggest that long range interactions between boundary edges and areas enclosed by them, such that diffusion-based models describe, provide a much more plausible account for these brightness phenomena, and local models are insufficient.     

Differences in functional organization of the visual center in frogs and cats

Functional characteristics of responses of tectal neurons in the frog and the primary visual cortex of the cat obtained under indentical experimental conditions during changes in the brightness and duration of flashes within the range of 6 log units were compared. In frogs most units have short summation times and relatively lower thresholds; the response latency is 5–7 times longer than in cats. The overwhelming majority of tectal units can respond only to a narrow range of photic energy that differs for different cells. Most cells in cats respond to changes in brightness of between 4 and 5 log units; they have long summation times, short latent periods, and relatively higher thresholds. The differences found on comparison of the various functional characteristics of the cells in the visual center show that frogs have fixed mechanisms of temporal and spatial interaction responsibile for detection of stimulus brightness. In cats this interaction between individual cell populations and this mutual inhibition between adjacent cells are not prominent. The increased complexity and overlapping of interneuronal connections leads to convergence of day and twilight vision stimuli on the same neuron and to the ability of single units to respond to the whole "working" range of light brightness for the cat visual system.     

What are lightness illusions and why do we see them?

Lightness illusions are fundamental to human perception, and yet why we see them is still the focus of much research. Here we address the question by modelling not human physiology or perception directly as is typically the case but our natural visual world and the need for robust behaviour. Artificial neural networks were trained to predict the reflectance of surfaces in a synthetic ecology consisting of 3-D “dead-leaves” scenes under non-uniform illumination. The networks learned to solve this task accurately and robustly given only ambiguous sense data. In addition—and as a direct consequence of their experience—the networks also made systematic “errors” in their behaviour commensurate with human illusions, which includes brightness contrast and assimilation—although assimilation (specifically White's illusion) only emerged when the virtual ecology included 3-D, as opposed to 2-D scenes. Subtle variations in these illusions, also found in human perception, were observed, such as the asymmetry of brightness contrast. These data suggest that “illusions” arise in humans because (i) natural stimuli are ambiguous, and (ii) this ambiguity is resolved empirically by encoding the statistical relationship between images and scenes in past visual experience. Since resolving stimulus ambiguity is a challenge faced by all visual systems, a corollary of these findings is that human illusions must be experienced by all visual animals regardless of their particular neural machinery. The data also provide a more formal definition of illusion: the condition in which the true source of a stimulus differs from what is its most likely (and thus perceived) source. As such, illusions are not fundamentally different from non-illusory percepts, all being direct manifestations of the statistical relationship between images and scenes.     

Neurophysiological mechanisms underlying face processing within and beyond the temporal cortical visual areas.

The ways in which information about faces is represented and stored in the temporal lobe visual areas of primates, as shown by recordings from single neurons in macaques, are considered. Some neurons that respond primarily to faces are found in the cortex in the anterior part of the superior temporal sulcus (in which neurons are especially likely to be tuned to facial expression and to face movement involved in gesture), and in the TE areas more ventrally forming the inferior temporal gyrus (in which neurons are more likely to have responses related to the identity of faces). Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding rather than 'grandmother cell' encoding is used. It is argued that this type of tuning is a delicate compromise between very fine tuning, which has the advantage of low interference in neuronal network operations but the disadvantage of losing the useful properties (such as generalization, completion and graceful degradation) of storage in neuronal networks, and broad tuning, which has the advantage of allowing these properties of neuronal networks to be realized but the disadvantage of leading to interference between the different memories stored in an associative network. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations that is built is object based, which is suitable for recognition and as an input to associative memory, and that another is viewer centred, which is appropriate for conveying information about gesture. Ways are considered in which such cortical representations might be built by competitive self-organization aided by back projections in the multi-stage cortical processing hierarchy which has convergence from stage to stage.     

Stereoscopic subsystems for position in depth and for motion in depth.

We describe psychophysical evidence that the human visual system contains information-processing channels for motion in depth in addition to those for position in depth. These motion-in-depth channels include some that are selectively sensitive to the relative velocities of the left and right retinal images. We propose that the visual pathway contains stereoscopic (cyclopean) motion filters that respond to only a narrow range of the directions of motion in depth. Turning to the single-neuron level we report that, in addition to neurons turned to position to depth, cat visual cortex contains neurons that emphasize information about the direction of motion at the expense of positional information. We describe psychophysical evidence for the existence of channels that are sensitive to change size, and are separate from the channels both for motion and for flicker. These changing-size channels respond independently of whether the stimulus is a bright square on a dark ground or a dark square on a bright ground. At the physiological level we report single neurons in cat visual cortex that respond selectively to increasing or to decreasing size independently of the sign of stimulus contrast. Adaptation to a changing-size stimulus produces two separable after-effects: an illusion of changing size, and an illusion of motion in depth. These after-effects have different decay time constants. We propose a psychophysical model in which changing-size filters feed a motion-in-depth stage, and suppose that the motion-in-depth after-effect is due to activity at the motion-in-depth stage, while the changing-size after-effect is due to to activity at the changing-size and more peripheral stages. The motion-in-depth after-effect can be cancelled either by a changing-size test stimulus or by relative motion of the left and right retinal images. Opposition of these two cues can also cancel the impression of motion in depth produced by the adapting stimulus. These findings link the stereoscopic (cyclopean) motion filters and the changing-size filters: both feed the same motion-in-depth stage.     

Visibility reflects dynamic changes of effective connectivity between V1 and fusiform cortex

Identifying the neural basis of visibility is central to understanding conscious visual perception. Visibility of basic features such as brightness is often thought to reflect activity in just early visual cortex. But here we show under metacontrast masking that fMRI activity in stimulus-driven areas of early visual cortex did not reflect parametric changes in the visibility of a brightness stimulus. The psychometric visibility function was instead correlated with activity in later visual regions plus parieto-frontal areas, and surprisingly, in representations of the unstimulated stimulus surround for primary visual cortex. Critically, decreased stimulus visibility was associated with a regionally-specific decoupling between early visual cortex and higher visual areas. This provides evidence that dynamic changes in effective connectivity can closely reflect visual perception.     

Spatiotemporal dynamics of modality-specific and supramodal word processing

The ability of written and spoken words to access the same semantic meaning provides a test case for the multimodal convergence of information from sensory to associative areas. Using anatomically constrained magnetoencephalography (aMEG), the present study investigated the stages of word comprehension in real time in the auditory and visual modalities, as subjects participated in a semantic judgment task. Activity spread from the primary sensory areas along the respective ventral processing streams and converged in anterior temporal and inferior prefrontal regions, primarily on the left at around 400 ms. Comparison of response patterns during repetition priming between the two modalities suggest that they are initiated by modality-specific memory systems, but that they are eventually elaborated mainly in supramodal areas.     

Demonstration of interactions between visual and splanchnic afferences at the level of the cerebral cortex in cats]

In the chloralose-anesthetized cats, evoked potentials (E.P) were recorded from cerebral cortex with the use of 1) macroelectrodes in two overlapping zones between splanchnic and visual areas : Medial Lateral and Anterior Suprasylvian (S II) gyri ; 2) microelectrodes in Medial Lateral gyrus. Our results show : 1) a strong increase of the primary visual E.P. in Medial Laternal gyrus by splanchnic stimulus ; 2) a strong inhibition of the primary splanchnic E.P. in S II by visual stimulus ; 3) an inhibition of some cortical neurons in Medial Lateral gyrus by splanchnic stimulus ; 4) an inhibition of associative visual E.P. in S II by splanchnic stimulus, and of associative splanchnic E.P. in Medial Lateral gyrus by visual stimulus. In the other hand splanchnic and visual E.P. were recorded from N. reticularis and Corpus Geniculatum Mediale with the use of concentric electrode. Some hypothesis concerning interrelations mechanisms are discussed.     

Efferent connections of the nucleus lateralis posterior-pulvinar complex in the cat.

The nucleus lateralis posterior-pulvinar complex of the thalamus displays an integrative function. The efferent connections of this nuclear group were examined by the authors in the cat. In their work, they utilized also the earlier observations on the afferent connections of the nucleus. The nuclear complex projects to the associative fields encompassed by the visual- and the acoustic cortex without intruding into the primary cortical areas. On the other hand, its afferent connections are, apart from the associative field, also yielded by the primary visual and acoustic cortex. All this is completed by the reciprocal connections of the LP-pulvinar complex with the visual- and acoustic system, as well as between the associative areas of the cortex.     

The human brain from above: an increase in complexity from environmental stimuli to abstractions

Contrary to common belief, the brain appears to increase the complexity from the perceived object to the idea of it. Topological models predict indeed that: (a) increases in anatomical/functional dimensions and symmetries occur in the transition from the environment to the higher activities of the brain, and (b) informational entropy in the primary sensory areas is lower than in the higher associative ones. To demonstrate this novel hypothesis, we introduce a straightforward approach to measuring island information levels in fMRI neuroimages, via Rényi entropy derived from tessellated fMRI images. This approach facilitates objective detection of entropy and corresponding information levels in zones of fMRI images generally not taken into account. We found that the Rényi entropy is higher in associative cortices than in the visual primary ones. This suggests that the brain lies in dimensions higher than the environment and that it does not concentrate, but rather dilutes messages coming from external inputs.     

Orientation enhancement in early visual processing can explain time course of brightness contrast and White’s illusion

Dynamics of orientation tuning in V1 indicates that computational model of V1 should not only comprise of bank of static spatially oriented filters but also include the contribution for dynamical response facilitation or suppression along orientation. Time evolution of orientation response in V1 can emerge due to time- dependent excitation and lateral inhibition in the orientation domain. Lateral inhibition in the orientation domain suggests that Ernst Mach’s proposition can be applied for the enhancement of initial orientation distribution that is generated due to interaction of visual stimulus with spatially oriented filters and subcortical temporal filter. Oriented spatial filtering that appears much early ( $<$ 70 ms) in the sequence of visual information processing can account for many of the brightness illusions observed at steady state. It is therefore expected that time evolution of orientation response might be reflecting in the brightness percept over time. Our numerical study suggests that only spatio-temporal filtering at early phase can explain experimentally observed temporal dynamics of brightness contrast illusion. But, enhancement of orientation response at early phase of visual processing is the key mechanism that can guide visual system to predict the brightness by “Max-rule” or “Winner Takes All” (WTA) estimation and thus producing White’s illusions at any exposure.     

Am I seeing my hand? Visual appearance and knowledge of controllability both contribute to the visual capture of a person's own body

When confronted with complex visual scenes in daily life, how do we know which visual information represents our own hand? We investigated the cues used to assign visual information to one''s own hand. Wrist tendon vibration elicits an illusory sensation of wrist movement. The intensity of this illusion attenuates when the actual motionless hand is visually presented. Testing what kind of visual stimuli attenuate this illusion will elucidate factors contributing to visual detection of one''s own hand. The illusion was reduced when a stationary object was shown, but only when participants knew it was controllable with their hands. In contrast, the visual image of their own hand attenuated the illusion even when participants knew that it was not controllable. We suggest that long-term knowledge about the appearance of the body and short-term knowledge about controllability of a visual object are combined to robustly extract our own body from a visual scene.     

Changes in the evoked potentials in the visual and association cortex of the alert cat after changing the order of stimulation of the lateral geniculate body and superior colliculi

In chronic experiments on alert cats the preceding stimulation of the lateral geniculate body (LGB) facilitates the response in the visual cortex to testing stimulation of the anterior colliculi (AC) at all studied delays between stimuli in contrast to the associative cortex where this response has been depressed in intervals of 10-40 ms. In reverse order of stimulation, facilitation of response to testing LGB stimulation is observed at all studied delays in the associative cortex, while in the visual cortex this response is slightly depressed. The obtained data point to the importance of the information coming in the accessory zones of LGB and AC projections and to different informational value of AC inputs to the associative and visual cortices and reciprocal relations between inputs to these cortical areas from LGB and AC.     

A polysensory pathway to the forebrain of the pigeon: the ascending projections of the nucleus dorsolateralis posterior thalami (DLP).

Visual evoked potentials (VEPs) in the associative neostriatum caudolaterale (NCL) have shorter latencies than those recorded in other visual forebrain areas. Therefore visual input into NCL probably stems from a subtelencephalic relay. Tracing experiments revealed a projection of the nucleus dorsolateralis posterior thalami (DLP) into those portions of NCL in which visual, auditory, and somatosensory afferents from intratelencephalic parasensory areas terminate. Since VEPs in NCL are abolished after DLP-lesions, this structure has to be the critical relay. However, DLP also projects to other associative forebrain areas and parts of the basal ganglia. Previous experiments had furthermore revealed that DLP-neurons integrate visual, auditory, and somatosensory inputs. Thus, the DLP-projection onto various associative forebrain areas represents a true polysensory thalamotelencephalic system.     

Neural basis of the ventriloquist illusion

The ventriloquist creates the illusion that his or her voice emerges from the visibly moving mouth of the puppet [1]. This well-known illusion exemplifies a basic principle of how auditory and visual information is integrated in the brain to form a unified multimodal percept. When auditory and visual stimuli occur simultaneously at different locations, the more spatially precise visual information dominates the perceived location of the multimodal event. Previous studies have examined neural interactions between spatially disparate auditory and visual stimuli [2-5], but none has found evidence for a visual influence on the auditory cortex that could be directly linked to the illusion of a shifted auditory percept. Here we utilized event-related brain potentials combined with event-related functional magnetic resonance imaging to demonstrate on a trial-by-trial basis that a precisely timed biasing of the left-right balance of auditory cortex activity by the discrepant visual input underlies the ventriloquist illusion. This cortical biasing may reflect a fundamental mechanism for integrating the auditory and visual components of environmental events, which ensures that the sounds are adaptively localized to the more reliable position provided by the visual input.     

Stimulus size and the magnitude of the visual illusion of extent

Psychophysical experiments have been performed to study the dependence of the magnitude of the illusion of extent on the size of the referential part of the stimulus for different lengths of the imaginary wings of a modified Brentano figure. The experimental data are explained in terms of a model based on the concept of biases of the centroids of excitatory patterns evoked by stimulus terminating elements. A good fit of experimental data to calculated values confirms the model’s assumption that the areas of perceptual influence increase depend on their eccentricity in the visual field. An estimation of the model’s parameters also confirms the assumption that distortion of perceived information on the relative positioning of the centers of masses of the stimulus terminators is one of the main factors determining the magnitude of the illusion of extent and supports the hypothesis on the relationship of the phenomenon of this illusion with characteristics of the mechanism responsible for the perception of three-dimensional coordinates of visual objects.     

Mechanisms of Selective Attention during Competitive Discrimination of Visual and Auditory Verbal Information: Positron Emission Tomography and Cortical Evoked Potential Studies

The mechanisms of selective verbal attention were studied under conditions of simultaneous delivery of speech signals via the visual and auditory channels. The investigation was based on the comparison and synthesis of data obtained by two methods: positron emission tomography (PET) and brain evoked potentials (EPs). A new approach was developed: complementary tasks were constructed in such a way that, despite principal methodological problems, the same phenomenon could be investigated in one paradigm in EP and PET studies. The results obtained by the two methods are in rather good agreement with respect to topography: the secondary and tertiary areas, as well as the associative brain areas, are involved in attention concentration, that is, selection of verbal information occurs at the level of cognitive processes. The combination of two complementary methods, PET and EP, allowed the processes of processing of sensory information and brain mechanisms of selective attention to be investigated much more completely. The PET studies contributed to further understanding of brain mechanisms evidencing where processing occurs and the EP method provided insight into the mechanism of how this information is processed inside the corresponding cortical areas. The finding that the activation of primary areas of the visual cortex is accompanied by the inhibition of visual information deserves attention. This conclusion can be considered highly significant because of the concordance of the two independent methods. How to interpret it is not yet clear. It is possible that, in the case of primary importance of verbal information and priority of the visual channel for the repression from consciousness of artificially irrelevant information, a safety mechanism is activated: the amplified signal enters the brain cortex, where it is retained in the short-term iconic memory. This enables a reaction to this stimulus (if necessary), in the presence of any additional sign involving selective attention.     

Probing the Neural Basis of Perceptual Phenomenology with the Touch-Induced Visual Illusion

Using the touch-induced visual illusion we examine whether the brain regions involved in coding sensory information are dissociable from those that contain decision information. Activity in the intraparietal sulcus, as measured by functional magnetic resonance imaging, was associated with the illusion suggesting a sensory coding role whereas activity in the middle occipital gyrus differentially modulated activity according to the decisions made by subjects consistent with their reported perceptual phenomenology.