Stimulus repetition effects on texture-based visual search by pigeons.

Four experiments investigated the effects of within-session stimulus repetition on texture discrimination. Six pigeons (Columba livia) searched for a contrasting target region (color or shape) randomly embedded within a larger distractor region for food reinforcement. Experiment 1 found that repeating features of the distractors, but not those of the target, across trials increased the accuracy of target localization relative to baseline. Experiment 2 found that subsequently switching the identity of a repeated distractor feature to the target decreased accuracy. Experiment 3 found that the effects of repeating a distractor feature influenced search performance for at least 60 trials after this learning. Experiment 4 found that differential stimulus-outcome relations can produce control by repeated target features. The results are discussed in terms of the factors and strategies involved in the control of avian visual search behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dimensional organization and texture discrimination in pigeons.

Two experiments examined the influence of dimensional organization on pigeons' texture perception, using a simultaneous conditional discrimination procedure. Four pigeons were reinforced for pecking at a small group of target colored shape elements randomly located within a larger array of distractor elements. The target and distractor regions of feature displays differed consistently in color or shape, whereas in conjunctive displays these regions were formed by conjunctive mixtures of the 2 dimensions. In Exp 1, pigeons' target-detection accuracy was higher with feature than with conjunctive displays. In Exp 2, pigeons responded more accurately and humans responded more quickly with feature than with 2 variations of conjunctive displays. These results suggest that the early visual mechanisms mediating the perception of dimensional information are similar for both species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition and transfer of visual texture discriminations by pigeons.

Two experiments investigated texture discrimination in pigeons. In a simultaneous conditional-discrimination procedure, pigeons were reinforced for pecking at a small target region of identically colored form elements embedded in a larger region of distractor elements. These regions differed in either color or shape or differed redundantly in both dimensions. Pigeons readily acquired these discriminations and showed substantial positive discrimination transfer to new displays composed from novel recombinations of training colors and shapes, novel colors and shapes, and novel spatial organizations. The global organization of these displays appeared to be chief property mediating performance. This suggests that pigeons have mechanisms for perceptually grouping regions of similar colors and shapes, and these mechanisms may be similar to the preattentive visual mechanisms proposed for human texture segregation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of a moving distractor on the initiation of smooth-pursuit eye movements

As a step toward understanding the mechanism by which targets are selected for smooth-pursuit eye movements, we examined the behavior of the pursuit system when monkeys were presented with two discrete moving visual targets. Two rhesus monkeys were trained to select a small moving target identified by its color in the presence of a moving distractor of another color. Smooth-pursuit eye movements were quantified in terms of the latency of the eye movement and the initial eye acceleration profile. We have previously shown that the latency of smooth pursuit, which is normally around 100 ms, can be extended to 150 ms or shortened to 85 ms depending on whether there is a distractor moving in the opposite or same direction, respectively, relative to the direction of the target. We have now measured this effect for a 360 deg range of distractor directions, and distractor speeds of 5-45 deg/s. We have also examined the effect of varying the spatial separation and temporal asynchrony between target and distractor. The results indicate that the effect of the distractor on the latency of pursuit depends on its direction of motion, and its spatial and temporal proximity to the target, but depends very little on the speed of the distractor. Furthermore, under the conditions of these experiments, the direction of the eye movement that is emitted in response to two competing moving stimuli is not a vectorial combination of the stimulus motions, but is solely determined by the direction of the target. The results are consistent with a competitive model for smooth-pursuit target selection and suggest that the competition takes place at a stage of the pursuit pathway that is between visual-motion processing and motor-response preparation.     

Same-different texture discrimination and concept learning by pigeons.

Investigated the acquisition and transfer of a "same-different" conditional discrimination using multidimensional visual texture stimuli in pigeons. Using a choice task, 4 pigeons were reinforced for discriminating different displays, created from aggregated differences in element color or shape, from uniform displays, in which all elements were identical. Discrimination of these 2 display types was readily acquired by the pigeons when they were required to locate and peck the contrasting target region of the different displays. The pigeons showed high levels of discrimination transfer to novel texture stimuli both during acquisition and in 2 subsequent transfer tests. The results suggest that pigeons may be able to learn a generalized same-different concept when promoted by the use of large numbers of multielement stimuli during training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

NMDA and D2-like receptors modulate cognitive flexibility in a color discrimination reversal task in pigeons.

Reversal and extinction learning represent forms of cognitive flexibility that refer to the ability of an animal to alter behavior in response to unanticipated changes on environmental demands. A role for dopamine and glutamate in modulating this behavior has been implicated. Here, we determined the effects of intracerebroventricular injections in pigeons' forebrain of the D2-like receptor agonist quinpirole, the D2-like receptor antagonist sulpiride and the N-methyl-d-aspartate receptor antagonist AP-5 on initial acquisition and reversal of a color discrimination task. On day one, pigeons had to learn to discriminate two color keys. On day two, pigeons first performed a retention test, which was followed by a reversal of the reward contingencies of the two color keys. None of the drugs altered performance in the initial acquisition of color discrimination or affected the retention of the learned color key. In contrast, all drugs impaired reversal learning by increasing trials and incorrect responses in the reversal session. Our data support the hypothesis that D2-like receptor mechanisms, like N-methyl-d-aspartate receptor modulations, are involved in cognitive flexibility and relearning processes, but not in initial learning of stimulus-reward association. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motor activation without conscious discrimination in metacontrast masking.

Nine experiments investigated motor responses to geometric stimuli (a target and a distractor) preceded by masked primes. In congruent trials, the target was preceded by a smaller target-like shape and the distractor by a smaller distractor-like shape. In incongruent trials this arrangement was reversed. In neutral trials both primes were distractor-like shapes. Highly significant effects of these priming conditions on reaction time and error rate were found, although there was no conscious discrimination of primes, as assessed by a discrimination index (d′ or ds) not different from 0. This result subsisted under conditions of time pressure, feedback, practice, and financial incentive in the discrimination task. It remained unchanged under conditions in which the reaction time and discrimination tasks were blocked, alternated, randomly mixed, or combined on each trial. It is concluded that motor activation without conscious discrimination was demonstrated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional control during visual search: the effect of irrelevant singletons

Four experiments investigated whether a highly salient color singleton can be ignored during serial search. Observers searched for a target letter among nontarget letters and were instructed to ignore an irrelevant, highly salient color singleton that was either compatible or incompatible with the response to the target letter. The results indicate that it was possible to prevent attentional capture by the irrelevant singleton only when both the target and the distractor color were known. When either the color of the target or the color of the to-be-ignored singleton were varied over trials, the irrelevant singleton captured attention. The ability to selectively filter singleton distractors during serial search depends on the presence of an attentional set for a specific feature value of both target and distractor. In the absence of a consistently predictable feature value of both target and distractor, top-down control is not possible.     

Transsaccadic representation of layout: What is the time course of boundary extension?

How rapidly does boundary extension occur? Across experiments, trials included a 3-scene sequence (325 ms/picture), masked interval, and repetition of 1 scene. The repetition was the same view or differed (more close-up or wide angle). Observers rated the repetition as same as, closer than, or more wide angle than the original view on a 5-point scale. Masked intervals were 100, 250, 625, or 1,000 ms in Experiment 1 and 42, 100, or 250 ms in Experiments 2 and 3. Boundary extension occurred in all cases: Identical views were rated as too "close-up," and distractor views elicited the rating asymmetry typical of boundary extension (wider angle distractors were rated as being more similar to the original than were closer up distractors). Most important, boundary extension was evident when only a 42-ms mask separated the original and test views. Experiments 1 and 3 included conditions eliciting a gaze shift prior to the rating test; this did not eliminate boundary extension. Results show that boundary extension is available soon enough and is robust enough to play an on-line role in view integration, perhaps supporting incorporation of views within a larger spatial framework. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional capture by salient color singleton distractors is modulated by top-down dimensional set.

Three experiments examined whether salient color singleton distractors automatically interfere with the detection singleton form targets in visual search (e.g., J. Theeuwes, 1992), or whether the degree of interference is top-down modulable. In Experiments 1 and 2, observers started with a pure block of trials, which contained either never a distractor or always a distractor (0% or 100% distractors)--varying the opportunity to learn distractor suppression. In the subsequent trial blocks, the proportion of distractors was systematically varied (within-subjects factor in Experiment 1, between-subjects factor in Experiment 2)--varying the incentive to use distractor suppression. In Experiment 3, observers started with 100% distractors in the first block and were presented with "rare" color or luminance distractors, in addition to "frequent" color distractors, in the second block. The results revealed distractor interference to vary as a function of both the initial experience with distractors and the incentive to suppress them: the interference was larger without relevant practice and with a lesser incentive to apply suppression (Experiments 1-3). This set of findings suggests that distractor interference is top-down modulable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Velocity-based motion categorization by pigeons.

To examine if animals could learn action-like categorizations in a manner similar to noun-based categories, eight pigeons were trained to categorize rates of object motion. Testing 40 different objects in a go/no-go discrimination, pigeons were first trained to discriminate between fast and slow rates of object rotation around their central y-axis. They easily learned this velocity discrimination and transferred it to novel objects and rates. This discrimination also transferred to novel types of motions including the other two axes of rotation and two new translations around the display. Comparable tests with rapid and slow changes in the objects' size, color, and shape failed to support comparable transfer. This difference in discrimination transfer between motion-based and property-based changes suggests the pigeons had learned motion concept rather than one based on change per se. The results provide evidence that pigeons can acquire an understanding of motion-based actions, at least with regard to the property of object velocity. This may be similar to our use of verbs and adverbs to categorize different classes of behavior or motion (e.g., walking, jogging, or running slow vs. fast). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Differential effects of visual context on pattern discrimination by pigeons (Columba livia) and humans (Homo sapiens).

Three experiments examined the role of contextual information during line orientation and line position discriminations by pigeons (Columba livia) and humans (Homo sapiens). Experiment 1 tested pigeons' performance with these stimuli in a target localization task using texture displays. Experiments 2 and 3 tested pigeons and humans, respectively, with small and large variations of these stimuli in a same-different task. Humans showed a configural superiority effect when tested with displays constructed from large elements but not when tested with the smaller, more densely packed texture displays. The pigeons, in contrast, exhibited a configural inferiority effect when required to discriminate line orientation, regardless of stimulus size. These contrasting results suggest a species difference in the perception and use of features and contextual information in the discrimination of line information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditional same-different discrimination by pigeons: Acquisition and generalization to novel and few-item displays.

The authors explored whether pigeons can learn to discriminate simultaneously presented arrays of 16 identical (Same) visual items from arrays of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background. In one experiment, pigeons rapidly learned this task and, after training with arrays created from a 72-icon set, they exhibited nearly perfect transfer to novel testing arrays. In a second experiment, pigeons’ accuracy to 24-, 20-, 12-, and 8-icon arrays during later testing remained as high as accuracy to training arrays; although accuracy declined with 4- and 2-icon arrays, it was still significantly above chance. In both experiments, pigeons’ choice reaction time scores nicely complemented their choice accuracy scores. These results suggest that the conditional discrimination procedure is well suited to disclose same-different discrimination in pigeons and to elucidate the interaction between perception and abstraction in conceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual half-field Stroop effects with spatial separation of words and color targets

Past inconsistencies in the occurrence of differential visual half-field Stroop effects were addressed in two experiments using a visual half-field presentation technique incorporating brief displays (100 ms) and a fixation task designed to ensure proper eye fixation at display onset. Experiment 1 used displays in which distractor words and color targets were presented in contralateral visual fields. Experiment 2 compared contralateral with ipsilateral displays where words and color targets appeared one above the other in the same visual field. Stroop effects were larger whenever a word occupied the right as opposed to the left visual field, regardless of whether the color target was left or right. Results are consistent with the idea that words are processed more efficiently or automatically in right visual field/left hemisphere presentations.     

Episodic retrieval in negative priming and repetition priming.

Subjects identified target letters flanked by incompatible distractor letters (e.g., ABA). Distractor onset was randomly simultaneous with target onset or was delayed by 400 ms. In Experiment 1, one third of probe-trial targets were identical to the preceding prime-trial distractor. Responses were slower to repeated letters than to unrepeated letters (negative priming) only when prime and probe trials shared the same distractor-onset conditions. In Experiment 2, one third of probe-trial targets were identical to the preceding prime-trial target. Significant facilitation (repetition priming) occurred for repeated targets in all conditions but was again greater when prime and probe trials shared the same distractor-onset conditions. The results strongly support episodic retrieval theories of both negative priming and repetition priming and suggest that a common mechanism underlies both phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Kinetics of AMPA-type glutamate receptor channels in rat caudate-putamen neurones show a wide range of desensitization but distinct recovery characteristics

In 5 experiments the authors examine the role of object-based grouping on negative priming. The experiments used a letter-matching task with multiple letters presented in temporally separated prime and probe displays. On mismatch trials, distractor letters in primes were repeated as targets in probes, or distractor and target letters were completely different. Negative priming was shown by slowed responses when distractors were repeated as targets relative to when the stimuli differed. This occurred both when only letters were presented (Experiments 1 and 4) and when letters were surrounded by boxes (Experiment 5). Experiments 2, 3, and 4 showed that negative priming was affected by the grouping of target and distractor letters in prime displays. Negative priming was reduced when 1 of the distractor letters was placed in the target box and 1 was left outside the box; facilitatory priming was observed when both distractor letters appeared in the target box. The data were accounted for in terms of there being (a) object-based competition for visual selection, (b) inhibition of distractor objects that compete for selection with target objects, and (c) activation or inhibition of the identities of all component elements within target or distractor objects.     

Pigeon same–different concept learning with multiple stimulus classes.

Two experiments examined the acquisition and transfer of a complex same–different discrimination by pigeons. With the use of a 2-alternative choice task, 5 pigeons were reinforced for discriminating odd-item Different displays, in which a contrasting target was present, from Same displays, in which all elements were identical. Four different types of same-different displays were concurrently tested. The display types differed in their configuration (texture vs. visual search organization), the nature of their elements (small and large colored shapes; pictures of birds, flowers, fish, and humans), and the processing demands required by their global-local element arrangement. Despite these differences, the pigeons learned to discriminate all 4 display types at the same rate and showed positive discrimination transfer to novel examples of each type, suggesting that a single generalized rule was used to discriminate all display types. These results provide some of the strongest evidence yet that pigeons, like many primates, can learn an abstract, visually mediated same-different concept. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object-based perceptual grouping affects negative priming.

In 5 experiments the authors examine the role of object-based grouping on negative priming. The experiments used a letter-matching task with multiple letters presented in temporally separated prime and probe displays. On mismatch trials, distractor letters in primes were repeated as targets in probes, or distractor and target letters were completely different. Negative priming was shown by slowed responses when distractors were repeated as targets relative to when the stimuli differed. This occurred both when only letters were presented (Experiments 1 and 4) and when letters were surrounded by boxes (Experiment 5). Experiments 2, 3, and 4 showed that negative priming was affected by the grouping of target and distractor letters in prime displays. Negative priming was reduced when 1 of the distractor letters was placed in the target box and 1 was left outside the box; facilitatory priming was observed when both distractor letters appeared in the target box. The data were accounted for in terms of there being (a) object-based competition for visual selection, (b) inhibition of distractor objects that compete for selection with target objects, and (c) activation or inhibition of the identities of all component elements within target or distractor objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same–different texture discrimination in pigeons: Testing competing models of discrimination and stimulus integration.

The choice behavior of 6 pigeons performing a multidimensional same-different texture discrimination was examined. On each trial, they had to choose among 2 choice hoppers depending on whether a color, shape, or redundant (color and shape) target signal was present or not in a textured stimulus. Receiver operating characteristic (ROC) curves were produced by variations in the a priori signal presentation probabilities across conditions. Quantitative analyses of these ROC curves were used to evaluate different competing theories of discrimination (signal detection vs. high-threshold-default response models) and information integration (independent observations, additive integration, unidimensional models). The results suggested the structure of the pigeons' choice behavior in this same different discrimination was best described by an unequal variance signal detection model involving a unidimensional evidence variable (e.g., degree of difference). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relative importance of location and feature cues for homing pigeon (Columba livia) goal recognition.

Homing pigeons were raised and trained in two lofts that differed with respect to their color features and location in space. During training, pigeons displayed accurate site preference for a particular loft. When tested for loft preference with the feature cues switched between the 2 lofts, the pigeons returned to the loft that occupied the correct location. In a 2nd experiment, pigeons were trained to find food hidden in I of 4 color bowls (feature cues) located next to a landmark beacon (proximal spatial cue) in a constant location in a room (distal spacial cues). On test trials, pigeons chose the bowl at the correct location in the room if either the color bowl or the beacon was moved by itself but chose the correct color bowl next to the beacon if they were moved together. Together, the data suggest that the importance of location and feature information for goal recognition may be context specific. (PsycINFO Database Record (c) 2010 APA, all rights reserved)