Classes Of Visual Stimuli Research Articles

Beyond visual integration: sensitivity of the temporal-parietal junction for objects, places, and faces

One important role of the TPJ is the contribution to perception of the global gist in hierarchically organized stimuli where individual elements create a global visual percept. However, the link between clinical findings in simultanagnosia and neuroimaging in healthy subjects is missing for real-world global stimuli, like visual scenes. It is well-known that hierarchical, global stimuli activate TPJ regions and that simultanagnosia patients show deficits during the recognition of hierarchical stimuli and real-world visual scenes. However, the role of the TPJ in real-world scene processing is entirely unexplored. In the present study, we first localized TPJ regions significantly responding to the global gist of hierarchical stimuli and then investigated the responses to visual scenes, as well as single objects and faces as control stimuli. All three stimulus classes evoked significantly positive univariate responses in the previously localized TPJ regions. In a multivariate analysis, we were able to demonstrate that voxel patterns of the TPJ were classified significantly above chance level for all three stimulus classes. These results demonstrate a significant involvement of the TPJ in processing of complex visual stimuli that is not restricted to visual scenes and that the TPJ is sensitive to different classes of visual stimuli with a specific signature of neuronal activations.

A comparative study on classification of magnetoencephalography signals using probabilistic neural network and multilayer neural network

Visual decoding is a critical way to understand the face perception mechanism of the brain in the neuroscience field. Magnetoencephalography (MEG) is a completely noninvasive measurement technique that provides information about brain cortical functioning using the magnetic field of neuronal electrical activity. These neuromagnetic signals measured by MEG may emerge as a result of a visual stimulus during the brain decoding process for the face perception mechanism. In this research study, two classes of visual stimuli (face/scrambled face), including 9414 trials in total, were used. In order to obtain meaningful data from noisy MEG recordings, feature extraction approaches and classification systems are required. For the purpose of feature extraction, the Riemannian approach, characterized by its competitive nature, has been used. A probabilistic neural network and a multilayer neural network structures were proposed to classify magnetoencephalography signals. The obtained results were presented comparatively with the results of prior studies using the same dataset. The classification accuracies of 82.36% and 77.78% were achieved for the probabilistic neural network and multilayer neural network, respectively. Moreover, the probabilistic neural network classifier could be expected to be an alternative method to other competing methods. Because PNN does not use the back-propagation algorithm, so there is no need to train the network with the whole dataset. Thus, the classification process is performed faster.

Could Face Presence In Print Ads Influence Memorization?

<p>A large amount of literature in psychology and neurosciences demonstrates that attention is preferentially and automatically oriented toward faces. This stimulus is fixed longer and processed faster compared to other classes of visual stimuli (objects). This article investigates if and how face presence in print ads affects the memorization of ads content. A folder test procedure was used where ads, with or without faces, were inserted. Findings suggest that face presence in ads image positively influences ads memorization. Implications for advertising conception and promotion campaigns are discussed.</p>

The role of biological motion in audio-visual integration

• Dynamic visual stimuli induce a more salient illusion than their static counterparts. • This may help explain the striking contrast between the original illusion (Schutz & Lipscomb, 2007) and the literature on audio-visual integration, which generally reports visual dominance in such tasks. • At this time we are still unsure why blocking structure plays such a key role, and plan to investigate this in subsequent experiments. Stimuli • Two classes of visual stimuli: • dynamic dots (illustrating movement outlined in Fig. 2) • static dots (stationary dots lasting 500 or 1000 ms). • Participants were instructed to indicate perceived note duration of the heard sound, ignoring visual information • Sounds were pure tones synthesized with piano-like amplitude envelopes (i.e. exponentially decaying immediately after onset completion)

The fusiform response to faces: Explicit versus implicit processing of emotion

Regions of the fusiform gyrus (FG) respond preferentially to faces over other classes of visual stimuli. It remains unclear whether emotional face information modulates FG activity. In the present study, whole-head magnetoencephalography (MEG) was obtained from fifteen healthy adults who viewed emotionally expressive faces and made button responses based upon emotion (explicit condition) or age (implicit condition). Dipole source modeling produced source waveforms for left and right primary visual and left and right fusiform areas. Stronger left FG activity (M170) to fearful than happy or neutral faces was observed only in the explicit task, suggesting that directed attention to the emotional content of faces facilitates observation of M170 valence modulation. A strong association between M170 FG activity and reaction times in the explicit task provided additional evidence for a role of the fusiform gyrus in processing emotional information.

Physiological clustering of visual channels in the mouse retina

Anatomy predicts that mammalian retinas should have in excess of 12 physiological channels, each encoding a specific aspect of the visual scene. Although several channels have been correlated with morphological cell types, the number of morphological types generally exceeds the known physiological types. Here, we attempted to sort the ganglion cells of the mouse retina purely on a physiological basis. The null hypothesis was that the outputs of the ganglion cells form a continuum or should be divided into only a few types. We recorded the spiking output of 471 retinal ganglion cells on a multielectrode array while presenting 4 classes of visual stimuli. Five parameters were chosen to describe each cell's response characteristics, including relative amplitude of the ON and OFF responses, response latency, response transience, direction selectivity, and the receptive field surround. We compared the results of four clustering routines and judged the results using the relevant validation indices. The optimal partition was the 12-cluster solution of the Fuzzy Gustafson-Kessel algorithm. This classification contained three visual channels that carried predominately OFF responses, six that carried ON responses, and three that carried both ON and OFF information. They differed in other parameters as well. Other evidence suggests that the true number of cell types in the mouse retina may be somewhat larger than 12, and a definitive typology will probably require broader stimulus sets and characterization of more response parameters. Nonetheless, the present results do allow us to reject the null hypothesis: it appears that in addition to well-known cell types (such as the ON-OFF direction selectivity cells) numerous other cell classes can be identified in the mouse retina based solely on their responses to a standard set of simple visual stimuli.

Modulation of Temporal Precision in Thalamic Population Responses to Natural Visual Stimuli

Natural visual stimuli have highly structured spatial and temporal properties which influence the way visual information is encoded in the visual pathway. In response to natural scene stimuli, neurons in the lateral geniculate nucleus (LGN) are temporally precise – on a time scale of 10–25 ms – both within single cells and across cells within a population. This time scale, established by non stimulus-driven elements of neuronal firing, is significantly shorter than that of natural scenes, yet is critical for the neural representation of the spatial and temporal structure of the scene. Here, a generalized linear model (GLM) that combines stimulus-driven elements with spike-history dependence associated with intrinsic cellular dynamics is shown to predict the fine timing precision of LGN responses to natural scene stimuli, the corresponding correlation structure across nearby neurons in the population, and the continuous modulation of spike timing precision and latency across neurons. A single model captured the experimentally observed neural response, across different levels of contrasts and different classes of visual stimuli, through interactions between the stimulus correlation structure and the nonlinearity in spike generation and spike history dependence. Given the sensitivity of the thalamocortical synapse to closely timed spikes and the importance of fine timing precision for the faithful representation of natural scenes, the modulation of thalamic population timing over these time scales is likely important for cortical representations of the dynamic natural visual environment.

Naming and equivalence: Response latencies for emergent relations

In an attempt to distinguish between associative network and verbal mediation accounts of equivalence formation, three experiments were carried out in which conditional stimulus relations were established and response latencies assessed during tests for emergent relations. In Experiment 1, three groups of adults were trained with six three-member classes of visual stimuli, using different kinds of stimuli for each group: readily nameable pictograms, which were “preassociated” (Group 1); equally nameable but “non-associated” pictograms (Group 2); or non-associated “abstract” stimuli, designed to discourage the use of verbal mediators (Group 3). For those trained with pictograms, equal response latencies were observed on all tested relations, viz. trained associations, symmetry, transitivity, and transitivity with symmetry, but for subjects given abstract stimuli response latencies were greater on tests requiring transitivity. In Experiment 2 this result was replicated with methodological refinements, using...

Neocortical Connectivity during Episodic Memory Formation

During the formation of new episodic memories, a rich array of perceptual information is bound together for long-term storage. However, the brain mechanisms by which sensory representations (such as colors, objects, or individuals) are selected for episodic encoding are currently unknown. We describe a functional magnetic resonance imaging experiment in which participants encoded the association between two classes of visual stimuli that elicit selective responses in the extrastriate visual cortex (faces and houses). Using connectivity analyses, we show that correlation in the hemodynamic signal between face- and place-sensitive voxels and the left dorsolateral prefrontal cortex is a reliable predictor of successful face–house binding. These data support the view that during episodic encoding, “top-down” control signals originating in the prefrontal cortex help determine which perceptual information is fated to be bound into the new episodic memory trace.

Neural responses to polar, hyperbolic, and Cartesian gratings in area V4 of the macaque monkey.

1. We studied the responses of 103 neurons in visual area V4 of anesthetized macaque monkeys to two novel classes of visual stimuli, polar and hyperbolic sinusoidal gratings. We suspected on both theoretical and experimental grounds that these stimuli would be useful for characterizing cells involved in intermediate stages of form analysis. Responses were compared with those obtained with conventional Cartesian sinusoidal gratings. Five independent, quantitative analyses of neural responses were carried out on the entire population of cells. 2. For each cell, responses to the most effective Cartesian, polar, and hyperbolic grating were compared directly. In 18 of 103 cells, the peak response evoked by one stimulus class was significantly different from the peak response evoked by the remaining two classes. Of the remaining 85 cells, 74 had response peaks for the three stimulus classes that were all within a factor of 2 of one another. 3. An information-theoretic analysis of the trial-by-trial responses to each stimulus showed that all but two cells transmitted significant information about the stimulus set as a whole. Comparison of the information transmitted about each stimulus class showed that 23 of 103 cells transmitted a significantly different amount of information about one class than about the remaining two classes. Of the remaining 80 cells, 55 had information transmission rates for the three stimulus classes that were all within a factor of 2 of one another. 4. To identify cells that had orderly tuning profiles in the various stimulus spaces, responses to each stimulus class were fit with a simple Gaussian model. Tuning curves were successfully fit to the data from at least one stimulus class in 98 of 103 cells, and such fits were obtained for at least two classes in 87 cells. Individual neurons showed a wide range of tuning profiles, with response peaks scattered throughout the various stimulus spaces; there were no major differences in the distributions of the widths or positions of tuning curves obtained for the different stimulus classes. 5. Neurons were classified according to their response profiles across the stimulus set with two objective methods, hierarchical cluster analysis and multidimensional scaling. These two analyses produced qualitatively similar results. The most distinct group of cells was highly selective for hyperbolic gratings. The majority of cells fell into one of two groups that were selective for polar gratings: one selective for radial gratings and one selective for concentric or spiral gratings. There was no group whose primary selectivity was for Cartesian gratings. 6. To determine whether cells belonging to identified classes were anatomically clustered, we compared the distribution of classified cells across electrode penetrations with the distribution that would be expected if the cells were distributed randomly. Cells with similar response profiles were often anatomically clustered. 7. A position test was used to determine whether response profiles were sensitive to precise stimulus placement. A subset of Cartesian and non-Cartesian gratings was presented at several positions in and near the receptive field. The test was run on 13 cells from the present study and 28 cells from an earlier study. All cells showed a significant degree of invariance in their selectivity across changes in stimulus position of up to 0.5 classical receptive field diameters. 8. A length and width test was used to determine whether cells preferring non-Cartesian gratings were selective for Cartesian grating length or width. Responses to Cartesian gratings shorter or narrower than the classical receptive field were compared with those obtained with full-field Cartesian and non-Cartesian gratings in 29 cells. Of the four cells that had shown significant preferences for non-Cartesian gratings in the main test, none showed tuning for Cartesian grating length or width that would account for their non-Cartesian res

Stimulus-dependent oscillations in the cat visual cortex: differences between bar and grating stimuli

We have investigated the dependence of cortical oscillations on the type of visual stimulus. Single unit recordings were performed in areas 17 and 18 of the cat visual cortex. Among 217 cortical neurons oscillations in the frequency range of 22–102 Hz were found in 29 cells (13%). The proportion of oscillating cells was higher (16%) if both bar and grating stimuli were used to stimulate cortical neurons. It was found that gratings are more effective than bars in triggering oscillatory patterns in cortical cells. Among 21 oscillating cells which were stimulated with both bar and grating stimuli, oscillations evoked with gratings were found in 17 neurons (81%) while oscillations evoked with bar stimuli were triggered in 7 cells (33%). The distributions of oscillation frequencies were statistically different for oscillations evoked with bars and gratings. Frequencies of oscillations evoked with bars were in the lower and higher range than frequencies of oscillations evoked with gratings. In 3 cells (14%), rhythmic patterns could be evoked with both bar and grating stimuli. However, the oscillations were of different frequencies. No significant correlation was found between the strength of oscillations and firing rate of cortical neurons. Both simple and complex cells manifested the same dependence on stimulus type. However, complex cells mostly exhibited oscillations in the lower frequency range while simple cells did so when neurons were stimulated with bars. The results suggest that various classes of visual stimuli can be coded by a temporal pattern of cortical responses.

Visual object agnosia without prosopagnosia or alexia: Evidence for hierarchical theories of visual recognition

Abstract A single case study is presented of a patient, Mr. W, with a selective deficit in recognizing pictures and real objects, linked to impaired stored visual knowledge about objects. Despite this, Mr. W maintained a preserved ability both to read aloud printed words and to recognize famous faces, when compared with age-matched control subjects. In addition, his access to semantic information from words was superior to that from pictures. The data provide evidence that visual agnosia can occur without alexia or prosopagnosia, contrary to recent proposals (Farah 1990, 1991). This finding is consistent with a hierarchical model of visual object recognition in which agnosia can reflect impaired stored knowledge of objects without accompanying perceptual deficits. The selective recognition deficit for objects further indicates that stored knowledge concerning different classes of visual stimuli (common objects, faces, and words) is separately represented in the brain.

Separable Mechanisms in Face Processing: Evidence from Hemispheric Specialization

This article addresses three issues in face processing: First, is face processing primarily accomplished by the right hemisphere, or do both left- and right-hemisphere mechanisms play important roles? Second, are the mechanisms the same as those involved in general visual processing, or are they dedicated to face processing? Third, how can the mechanisms be characterized more precisely in terms of processes such as visual parsing? We explored these issues using the divided visual field methodology in four experiments. Experiments 1 and 2 provided evidence that both left- and right-hemisphere mechanisms are involved in face processing. In Experiment 1, a right-hemisphere advantage was found for both Same and Different trials when Same faces were identical and Different faces differed on all three internal facial features. Experiment 2 replicated the right-hemisphere advantage for Same trials but showed a left-hemisphere advantage for Different trials when one of three facial features differed between the target and the probe faces. Experiment 3 showed that the right-hemisphere advantage obtained with upright faces in Experiment 2 disappeared when the faces were inverted. This result suggests that there are right-hemisphere mechanisms specialized for processing upright faces, although it could not be determined whether these mechanisms are completely face-specific. Experiment 3 also provided evidence that the left-hemisphere mechanisms utilized in face processing tasks are general-purpose visual mechanisms not restricted to particular classes of visual stimuli. In Experiment 4, a left-hemisphere advantage was obtained when the task was to find one facial feature that was the same between the target and the probe faces. We suggest that left-hemisphere advantages shown in face processing are due to the parsing and analysis of the local elements of a face.

Areal influences on complex cells in cat striate cortex: stimulus-specificity of width and length summation

In single neurones recorded from the striate cortex of cats anaesthetized with N2O/O2/halothane, receptive field dimensions, length specificity and areal extent of drive were assessed for different classes of visual stimuli. Receptive fields were mapped as rectangular minimum response fields (MRFs). Spatial summation along the axis of preferred orientation was assessed: for moving bars whose length was varied (length summation); and for height variation of a square-wave grating patch against a uniform grey background, or a patch of moving texture against a stationary background of similar texture. In complementary tests a moving square-wave grating background was progressively occluded by a uniform grey foreground mask of variable height; or a mask of stationary texture of variable height progressively occluded a background of moving texture. In parallel measurements, the width of grating or textured patches or masks was varied whilst maintaining height constant. Broadly speaking, the areal influence of each class of stimulus was comparable, and distinct from extra-receptive field phenomena in evoking responses from within the receptive field, but not from surrounding areas. The masking paradigm provided the most sensitive measure of receptive field height and width. However, in some neurones length summation, the degree of end-stopping, and the directional bias depended critically on the stimulus configuration used. Length summation tended to be more dramatic for short bars than for gratings. Length summation for texture was significantly more pronounced than for an oriented bar in special and in intermediate complex neurones. By contrast, endstopping was typically less intense for gratings than for bars, and least pronounced for texture. Because of stimulus specificity, complex neurones assigned to particular functional subgroups on the basis of their response to oriented bars may exhibit quite different patterns of behaviour for other classes of stimuli.

Upside-down faces: a review of the effect of inversion upon face recognition.

Several studies have found that face recognition is disproportionately impaired by stimulus inversion when compated to recognition of other classes of visual stimuli. This effect has been interpreted as evidence that face recognition benefits from a 'special' process which is not engaged by an inverted face. This paper reviews studies of the effect of inversion on face recognition in recognition memory tasks, matching tasks and upon cerebral hemisphere asymmetries. Evidence is drawn from developmental studies and from studies of brain-injured and normal adult subjects. It is concluded that the evidence that inverted faces are processed differently from upright faces is far from compelling, and therefore the effect of inversion provides little or no evidence of a unique process in face recognition. The inversion effect is interpreted in terms of expertise in face processing and the highly homogeneous nature of faces as a stimulus class.

Pornography and attitude change

Sexual arousal to erotica (Levitt, 1969) has long been the concern of several organized groups in our society. Various legislative bodies have, as a result of prodding from some of their constituents, reacted to this phenomenon by passing various laws. These acts are generally directed toward the definition and control of sexual arousal and toward the control of the stimulus materials which are presumed to promote the arousal states. In passing such legislation, legislatures have made several assumptions, the more important being: 1. Sexual arousal not in the service of reproduction is a social problem. 2. Sexual arousal to certain classes of stimuli is somehow qualitatively different from arousal due to other classes. 3. Exposure to certain classes of visual stimuli causes a decline in morals and an ensuring increase in antisocial ideation. These assumptions have been made, in the past, so as to justify such anti-obscenity measures as book-burning, boycotts, and legal controls. Of the latter, it has been said that: The very fact that every state, except one, as well as the federal government have passed some form of censorship law with respect to pornography is itself testimony independently given by many people over a long period of time that pornography does have some sort of influence. (Schmidt, 1957) Implied here is that obscenity does influence morals, behavior, or both, and that the various levels of government are acting upon evidence of this influence so as to protect the well-being of the people. The empirical evidence relating to the assumptions listed above, which are implicit in all obscenity statutes, was reviewed by Cairns, et al, (1961-1962) for the period 1925 to 1961. They found no direct test of the central assumption the causal relationship between exposure to obscene materials and anti-social behavior. A similar finding has been reported by Mann (1968). He reviewed the relevant literature for the period 1961 to 1968. Both authors reported that while sexual arousal may be induced by many diverse kinds of stimuli,

Fundamental properties of intensity, form, and motion perception in the visual nervous systems of Calliphora phaenicia and Musca domestica.

Several classes of interneurons in the optic lobes and brain of the insects, Musca domestica and Calliphora phaenicia, have been studied in detail. Visual stimuli have been categorized on the basis of the properties of intensity, form, and motion. Response characteristics of the classes of neural units are described with respect to these three classes of visual stimuli. While those units that detect motion in select directions have a tonic response, form detection units have a phasic response only. Through correlation of the responses of these classes with visual stimuli, it is shown that these units integrate the responses of other units which have very small visual fields. The small-field units are presumed to integrate the output of a small group of adjacent retinula cells and to respond differentially to intensity, form, and motion. It is shown that the response of both form and motion detection units is independent of the direction of pattern intensity gradation. As a consequence of this independence, it is further shown that failure to detect motion properly must start at a spatial wavelength four times the effective sampling station spacing rather than twice as has been predicted previously.