Pairs Of Visual Stimuli Research Articles

Stimulus Timing-Dependent Plasticity in Cortical Processing of Orientation

The relative timing of presynaptic and postsynaptic spikes plays a critical role in activity-induced synaptic modification. Here we examined whether plasticity of orientation selectivity in the visual cortex depends on stimulus timing. Repetitive pairing of visual stimuli at two orientations induced a shift in orientation tuning of cat cortical neurons, with the direction of the shift depending on the temporal order of the pair. Induction of a significant shift required that the interval between the pair fall within ±40 ms, reminiscent of the temporal window for spike timing-dependent synaptic plasticity. Mirroring the plasticity found in cat visual cortex, similar conditioning also induced a shift in perceived orientation by human subjects, further suggesting functional relevance of this phenomenon. Thus, relative timing of visual stimuli can play a critical role in dynamic modulation of adult cortical function, perhaps through spike timing-dependent synaptic plasticity.

Neuronal representations of stimulus associations develop in the temporal lobe during learning.

Visual stimuli that are frequently seen together become associated in long-term memory, such that the sight of one stimulus readily brings to mind the thought or image of the other. It has been hypothesized that acquisition of such long-term associative memories proceeds via the strengthening of connections between neurons representing the associated stimuli, such that a neuron initially responding only to one stimulus of an associated pair eventually comes to respond to both. Consistent with this hypothesis, studies have demonstrated that individual neurons in the primate inferior temporal cortex tend to exhibit similar responses to pairs of visual stimuli that have become behaviorally associated. In the present study, we investigated the role of these areas in the formation of conditional visual associations by monitoring the responses of individual neurons during the learning of new stimulus pairs. We found that many neurons in both area TE and perirhinal cortex came to elicit more similar neuronal responses to paired stimuli as learning proceeded. Moreover, these neuronal response changes were learning-dependent and proceeded with an average time course that paralleled learning. This experience-dependent plasticity of sensory representations in the cerebral cortex may underlie the learning of associations between objects.

Interhemispheric visual matching in the split brain

Three split-brained subjects, one (N.G.) with full forebrain commissurotomy and two (V.P. and J.W.) with callosotomy, made same-different judgments about pairs of visual stimuli that were flashed either unilaterally or bilaterally. In separate blocks of trials, the stimuli could differ in luminance, size, or color. In the bilateral condition, only J.W. scored above chance, and only minimally, on the luminance and size tasks, and none of the subjects scored above chance on the color task. Accuracy was generally much higher, especially for V.P. and J.W., when the stimuli were unilateral. These results confirm that there is little or no interhemispheric transfer of the visual attributes of luminance, size or color in the split brain.

Different systems in human brain are involved in presemantic discrimination of pictures as revealed by event-related potentials

It is uncertain if the several brain areas in response to presemantic picture processing are functionally homogeneous. Subjects were asked to discriminate visual stimulus pairs and event-related potentials (ERPs) were recorded from the scalp. A line-drawing picture (S1) was followed by another stimulus (S2) 600 ms later. S2 was the same as S1 in condition 1, a reversed picture of S1 in condition 2, the corresponding Chinese word in condition 3 and the syllabic alphabet of S1 in condition 4. Amplitudes of ERPs over right posterior scalp with time window from 102–180 ms after the onset of S2 in condition 1 and 2 were significantly larger than condition 3 and 4. The N2 component on the right anterolateral scalp with time window from 182–240 ms was significantly larger in condition 1 than other conditions, whereas the N2 on the left anterolateral scalp with time window from 262–350 ms in condition 2, 3 and 4 was significantly larger than condition 1. It is suggested that pictures and words are processed in different systems at the presemantic stage: repetitive and physically deviant stimuli evoke different responses in different brain regions.

Divided attention between simultaneous auditory and visual signals.

Past studies of simultaneous attention to pairs of visual stimuli have used the "dual-task" paradigm to show that identification of the direction of a change in luminance, whether incremental or decremental, is "capacity-limited," while simple detection of these changes is governed by "capacity-free" processes. On the basis of that finding, it has been suggested that the contrast between identification and detection reflects different processes in the sensory periphery, namely the responses of magno- and parvocellular receptors. The present study questions that assertion and investigates the contribution of central processing in resource limitation by applying the dual task to a situation in which one stimulus is auditory and one is visual. The results are much the same as before, with identification demonstrating the tradeoff in performance generally attributed to a limited capacity but detection showing no loss compared with single-task controls. This implies that limitations on resources operate at a central level of processing rather than in the auditory and visual peripheries.

Effects of amount of attention allocated to the location of visual stimulus pairs on perception of simultaneity.

This study was examined whether a change in the amount of attention equally allocated to two locations affects judgments of the simultaneity or successiveness of stimuli presented at those locations. Observers were cued to expect two brief flashes either to the left and right of fixation or above and below fixation. Stimulus onset asynchrony was randomly varied. On a small proportion of trials, the stimuli appeared at the unexpected locations. Observers were more likely to report the stimuli as simultaneous when they appeared in the unexpected locations. A model proposed to account for the data assumes that a brief stimulus event is represented by a probability distribution reflecting the uncertainty in determining the time of the event's occurrence, and two events are judged to be simultaneous if they are perceived to fall within some critical temporal interval, c, which is a function of the amount of attention allocated to the task.

Transitivity and Emergent Sequence Performances in Young Children

Children taught to sequence pairs of visual stimuli also performed additional sequences without direct training. In Experiment 1, the children were trained to produce a six-stimulus sequence (A > B > C > D > E > F) with one set of forms, and five overlapping two-stimulus sequences (A > B, B > C, C > D, D > E, and E > F) with another set of forms. Few of the children succeeded on tests for the untrained two- (e.g., B > D and B > E) and six-stimulus sequences derivable from the two-stimulus training. The children in Experiments 2 and 3 received only the overlapping sequence training before testing with refined protocols: Nearly all succeeded on tests of emergent sequences involving two, three, four, five, and six stimuli. The results suggest methods for examining transitive relations between pairs of the stimuli used in training and the development of a relation of order among all six of the stimuli involved.

Object discrimination learning and object-pattern discrimination transfer in visually deprived cats

We used binocularly deprived cats (BD cats), control cats reared in the laboratory with open eyes (C cats) and normal wild cats (N cats). In stage 1, the cats were trained to discriminate a black ping-pong ball and a 3-dimensional cross of the same size and color for food reward. The BD cats learned slower than N cats. The difference between BD cats and C cats was statistically insignificant. A comparison of these data and previous data on discrimination of corresponding 2-dimensional black patterns (disk and cross) show that in discrimination learning the 3-dimensionality of stimuli is helpful for N cats, but not for BD cats. Thus, the objects and their patterns are for BD cats highly similar. In stage 2, the objects were replaced by corresponding 2-dimensional patterns (disk and cross). Pattern discrimination was learned slower by BD cats than by N cats. Thus, the objects and their patterns are for BD cats certainly not identical and BD cats are deficient in discrimination transfer of even highly similar pairs of visual stimuli.

Different neural systems for the recognition of animals and man-made tools.

Using positron emission tomography, we mapped brain activity in normal volunteers during the recognition of visual stimuli representing living (animals) and non-living (artefacts) entities. The subjects had to decide whether pairs of visual stimuli were different representations of the same object, or different objects. Animal recognition was associated with activations in the inferior temporo-occipital areas, bilaterally, whereas artefact recognition engaged a predominantly left hemispheric network, involving the left dorsolateral frontal cortex. These findings, which concur with clinical observations in neurological patients, provide in vivo evidence for a fractionation of the neural substrates of semantic knowledge in man.

Effects of benzodiazepine receptor ligands on simultaneous visual discriminations of variable difficulty

Benzodiazepine receptor (BZR) ligands have been demonstrated to affect the performance in tasks measuring attentional abilities. In such tasks, subjects typically are required to discriminate visual and/or auditory stimuli. The possibility that the effects of BZR ligands on the performance in tasks measuring attention are primarily due to effects on discriminative processes has not been tested systematically. Rats were trained to discriminate between simultaneously presented pairs of visual stimuli flashing either at 5 Hz versus 4.17, 3.75, 2.5, 1.67 or 1.25 Hz (group 1; FAST), or at 1.25, 1.46, 1.67, 2.5 or 3.33 Hz versus 5 Hz (group 2; SLOW) for 4.8 s (20 trials per discrimination type; sequence of pairs was randomized). In both groups, response accuracy depended significantly on the discriminability of the stimuli, with near perfect accuracy in response to most different pairs of stimuli and near chance-level accuracy in response to least different pairs of stimuli. Administration of the BZR full agonist chlordiazepoxide (1.56, 6.25, 9.38 mg/kg; i.p.) potently increased the number of errors of omission which, following the higher doses, confounded the effects on absolute numbers of correct and incorrect responses. However, the available data do not suggest that the agonist affected the animals' abilities to discriminate between the stimuli. Similarly, administration of the BZR ligands ZK 93 426 and MDL 26,479 (which negatively modulate GABAergic transmission) produced no systematic effects. These data suggest that the effects of BZR ligands on the performance in tasks measuring attentional abilities are not primarily due to effects on the animals' ability to discriminate sensory stimuli.

Perceived Onset Simultaneity of Stimuli with Unequal Durations

Temporal-order judgment was investigated for a pair of visual stimuli with different durations in order to check whether offset asynchrony can disturb the perception of the order/simultaneity of onset. In experiment 1 the point of subjective simultaneity was estimated by the method of adjustment. The difference in duration of the two stimuli in the pair was either 0 or 50 ms. It was found that the subject shifts the onset of the shorter stimulus towards the offset of the longer one to obtain a satisfying impression of simultaneity even though the subject was asked to ignore the events concerning the stimulus offset. In experiments 2 and 3 the method of constant stimulus was applied. Both experiments indicate that subjects, in spite of instruction, take into account the offset asynchrony in their judgment.

Transitive inference formation in pigeons.

Pigeons were trained with 4 pairs of visual stimuli in a 5-term series―A+ B−, B+C, C+D→, and D+ E− (in which plus [+] denotes reward and minus [−] denotes nonreward)―before the unreinforced test pair B D was presented. All pigeons chose Item B, demonstrating inferential choice. A novel theory (value transfer theory), based on reinforcement mechanisms, is proposed. In experiment 2, the series was extended to 7 terms

A comparison of the effects of fornix transection and sulcus principalis ablation upon spatial learning by monkeys

In each of three experiments with Cynomolgus monkeys ( Macaca fascicularis), there was a group of normal control animals, a group with bilateral cortical ablations in the principal sulcus, and a group with fornix transection. In Expt. 1, half of each group learned problems in which the position of a pair of visual stimuli, to the monkey's left or right, indicated which of the visual stimuli was the correct (rewarded) one. The other animals learned problems in which visual stimuli indicated, irrespective of their own spatial position, whether reward was to be found on the monkey's left or on the right. The animals with fornix transection were impaired in both tasks. The animals with sulcus principalis ablation were also impaired in both tasks. The impairment caused by fornix transection was more severe than that caused by sulcus principalis ablation. Within each of the two operated groups, the degree of impairment in the two tasks was equal, when assessed in proportion to the difficulty of each task for control animals. Expt. 2 showed that neither of the operated groups was impaired in visual discrimination learning with spatial position irrelevant. Expt. 3 tested spatial discrimination learning (acquisition and reversal of a left-right discrimination) with irrelevant visual cues. Here the fornix-transected group was impaired but the group with sulcus principalis ablations was normal. It is suggested, on the basis of these findings and previous results, that fornix transection produces a general deficit in remembering the spatial arrangement of whole scenes, while sulcus principalis ablation produces a deficit in high-order integration involving spatial information.

ESTABLISHING AUDITORY STIMULUS CONTROL OVER AN EIGHT‐MEMBER EQUIVALENCE CLASS VIA CONDITIONAL DISCRIMINATION PROCEDURES

Two eight-member equivalence classes of visual stimuli were established during three phases of a training program. In Phase 1, two training arrangements were compared. In one, 3 subjects were taught on different trials to select from a single pair of comparison stimuli (A1, A2) in response to eight sample stimuli that were trained in pairs (B1, B2; C1, C2; D1, D2; E1, E2). In the second arrangement, subjects were taught to select from four pairs of comparisons (B1, B2; C1, C2; D3, D2; E2, E2) in response to two samples (A1, A2). Training with the single pair of comparison stimuli resulted in the development of equivalence relations (B1C1, B2C2, D1B1, D2B2, B1E1, B2E2, C1D1, C2D2, C1E1, C2E2, D1E1, D2E2, and their reciprocals) between the sample stimuli without direct training of these relations. In the other training arrangement, these relations among the comparison stimuli developed in the performance of 1 subject only. In Phase 2, three new pairs of stimuli (F1, F2; G1, G2; H1, H2) were substituted for three of the original pairs (B1, B2; C1, C2; D1, D2) and the training arrangements for the groups were reversed. Following training, the performances that showed equivalence relations on the probes in the first phase also showed equivalence relations in the second phase. If such relations did not develop in the first phase, they did not do so in the second phase. In Phase 3, relations between stimuli across the two previous phases (e.g., B1F1, B2F2, B1G1, B2H2, C1F1, etc.) were investigated. The 4 subjects whose performances showed the development of these relations were taught to select one stimulus from each class (E1 and E2) in response to a verbal label (I1 and I2) and then were tested to see if the verbal label controlled responding to the remaining members of the class (e.g., I1A1, I2A2, I1B1, I2B2, etc.). For 3 subjects, this generalized control occurred; for the 4th, generalization occurred only after verbal training with a second pair of visual stimuli (F1 and F2). In retests several months later, these auditory-visual relations were found to be intact or, if not, were recovered without direct training.

The effect of task parameters in diagnostic reading groups

This study compared the performance of normal, primary, and secondary reading groups on intersensory and intrasensory tasks requiring paired and serial recall. Auditory and visual stimulus pairs composed of digits from 1 to 9 were presented using a Bell and Howell Language Master. Eight experimental tasks (four intersensory and four intrasensory) that required paired and serial verbal recall with an alteration of the first recalled modality (auditory or visual) were used. Ten trials of each of the eight experimental conditions were used with three pairs of stimuli presented at 2-second intervals. Three types of recall errors were scored for each task: gross (omission or substitution of digits), order (digit out of sequence), and interchange (inversion of digits). A multivariate analysis of variance was carried out for the reading groups × tasks × error types. The level of recall errors on bisensory tasks (auditory and visual) was related to the reading diagnostic groups. All readers exhibit similar patterns in the processing of bisensory information; however, unique differences were found among normal, primary, and secondary readers. A summary profile is given of the effects of task parameters among the groups (normal, primary, and secondary readers) in the processing of bisensory tasks.

Consistent Responses by Groups of Subjects to Projective Differential Items

The nonverbal projective differential test item is described and distinguished from semantic differential items. Projective differential items are pairs of abstract visual stimuli, such as inkblots. Subjects choose one of the two projective stimuli as more similar to a concept being rated. Two studies showed that groups of subjects respond in a consistent manner to such items, with most subjects agreeing that one of the two abstract visual stimuli is more like the concept than the other; this is the projective differential response phenomenon. It was argued that subjects are able to express some aspects of the connotative meanings that concepts have for them through their responses to projective differential items. The potential usefulness of nonverbal items in constructing measuring instruments was discussed.

Functional significance of stimulus orientation: Effects on orientation discrimination

Children (6- and 9-year-olds) and adults were required to discriminate identical pairs of visual stimuli from mirror images. It was hypothesized that a key factor in performance would be the extent to which orientation was a functionally significant attribute of the stimuli. Two variables were manipulated, type of orientation discrimination and stimulus class. The first variable refers to the fact that the mirror images could be produced by either left/right or top/bottom reversals. Three classes of stimuli, varying in the extent to which a particular orientation was emphasized, were used: mobile objects (for which left/right orientation is assumed to be important); stationary objects (which lack comparable relevance for left/right orientation); and novel, abstract forms. The prediction was that if the discrimination task involved left/right reversals, as contrasted with top/bottom reversals, subjects would show an advantage for mobile objects, producing an interaction between stimulus class and orientation discrimination. In the first study, the subjects were children and performance was measured in terms of error rates. In the second study adults were tested, and reaction times were measured. Both studies manifested the predicted interaction. Results are discussed in terms of an information-processing framework, in which the incorporation of orientation-related features in the code representing a stimulus varies with the functional significance of the orientation to the stimulus class.

EXTENDING SEQUENCE‐CLASS MEMBERSHIP WITH MATCHING TO SAMPLE1

Three normal adults were first trained to point sequentially to each member of several pairs of visual stimuli. This baseline training established one class of stimuli to which subjects responded first, and another class of stimuli to which they responded second. Then, in a matching-to-sample procedure, baseline-sequence stimuli served as samples and new visual stimuli served as comparisons. Subjects were trained to choose one group of new comparisons when the sample was a "first" stimulus from the sequence baseline, and to choose the other new comparison stimuli when the sample was a "second" from the sequence baseline. When the new stimuli were then presented as pairs in the posttest, two subjects pointed to them in sequences predictable on the basis of the stimulus-class membership established during matching to sample. The failure of one subject to demonstrate sequential transfer was shown to be a consequence of the failure of the matching-to-sample procedure to establish stimulus classes. The production of sequences that were not directly trained suggested an empirical approach to the analysis of simple grammatical behavior.

Intensity and pattern discrimination after lesions of the pretectal complex, accessory optic nucleus and ventral geniculate in pigeons.

Pigeons were trained to discriminate between pairs of visual stimuli that differed in intensity or pattern. After completion of training, bilateral, stereotaxic lesions were made in various cell groups in the mesencephalon and diencephalon that receive terminals of the optic tract. The target regions were nucleus ectomamillaris (accessory optic nucleus), nucleus lentiformis mesencephali and area pretectalis (prectal complex) and the nucleus geniculatus lateralis, pars ventralis (ventral geniculate). In some cases, combined lesions of nucleus lentiformis mesencephali and area pretectalis were made. Lesions of nucleus ectomamillaris, nucleus lentiformis mesencephali, area pretectalis, or ventral geniculate did not produce major impairments of discrimination performance nor did combined lesions of nucleus lentiformis mesencephali and area pretectalis. A number of cases of intended destruction of the ventral geniculate also had extensive damage of the overlying nucleus rotundus. In several of these cases of combined destruction of nucleus rotundus and ventral geniculate, the previously reported discrimination deficits following nucleus rotundus lesions did not appear. In those cases in which the nucleus rotundus deficit was observed, the lesions were found to include the nucleus subpretectalis, which, like nucleus rotundus, receives tectofugal fibers via the brachium of the superior colliculus. The data of the ventral geniculate + rotundus cases and ventral geniculate + rotundus + subpretectalis cases suggest that sensory deficits following a lesion in a particular cell group may not necessarily indicate that the sensory information is processed in that cell group, but rather that the lesion had deprived other cell groups of the appropriate input necessary for their proper functioning.

The effect of an irrelevant dimension on "same-different" judgements of multi-dimensional stimuli.

Subjects made “same”-“different” judgements of simultaneously presented pairs of visual stimuli which could vary either in shape and colour independently, or in shape alone. In both conditions only shape was relevant to the “same”-“different” judgement. In the former condition “same” and “different” reaction times (RTs) were shorter when the states (“same” or “different”) of the relevant and the irrelevant dimension, colour, were the same. This result is interpreted as support for either a perceptual or a response interference hypothesis. The presence of an irrelevant dimension did not appear to affect differentially “same” and “different” judgements. The need for a re-evaluation of the results from other studies of multi-dimensional stimulus discrimination is discussed.