Restricted processing of simultaneously presented brightness and pattern stimuli in pigeons

Performance during simultaneous matching-to-sample was assessed in pigeons presented with element and compound visual samples. In Experiment 1, pigeons were trained with a symbolic matching procedure, in which different pairs of colored comparison cues presented on side keys were mapped onto a bright or dim houselight as one pair of sample stimuli and onto vertical and horizontal lines on the center key as a second pair of sample stimuli. They were then tested with houselight-line compound samples. It was found that matching accuracy for lines was significantly diminished with compound samples relative to element samples. Conversely, house-light intensities were matched as well with compound samples as with element samples. In Experiment 2, a similar effect was found with pigeons that had been trained to match only line samples. In Experiment 3, it was discovered that sample duration had no influence on the matching deficit found with lines following compound samples in birds either trained or not trained to match houselight intensities. These results, taken in combination with recent findings from experiments with auditory-visual compounds, suggest a restricted processing account of pigeon processing of simultaneously presented stimuli from different sources.     

Pigeons’ spatial memory: V. Proactive interference in the delayed matching of key location paradigm occurs only under restricted conditions

In the delayed matching of key location procedure, pigeons must remember the location of the sample key in order to choose correctly between two comparison keys. The deleterious effect of short intertrial intervals on key location matching found in previous studies suggested that pigeons’ short-term spatial memory is affected by proactive interference. However, because a reward expectancy mechanism may account for the intertriai interval effect, additional research aimed at demonstrating proactive interference was warranted. In Experiment 1, matching accuracy did not decline from early to late trials within a session, a finding inconsistent with a proactive interference effect. In Experiment 2, evidence suggestive of proactive interference was found: Matching was more accurate when the locations that served as distractors and as samples were chosen from different sets. However, this effect could have been due to differences in task difficulty, and the results of the two subsequent experiments provided no evidence of proactive interference. In Experiment 3, the distractor on Trialn was either the location that had served as the sample on Trialn ? 1 or one that had been a sample on earlier trials. Matching accuracy was not inferior on the former type of trial. In Experiment 4, the stimuli that served as samples and distractors were taken from sets containing 2, 3, 5, or 9 locations. Matching accuracy was no worse, actually slightly better, with smaller memory set sizes. Overall, these findings suggested that pigeons’ memory for spatial location may be immune to proactive interference. However, when, in Experiment 5, an intratrial manipulation was used, clear evidence of proactive interference was found: Matching accuracy was considerably lower when the sample was preceded by the distractor for that trial than when it was preceded by the sample or by nothing. Possible reasons why interference was produced by intratrial but not intertrial manipulations are discussed, as are implications of these data for models of pigeons’ short-term spatial memory.     

Short-term memory for visual and auditory stimuli in pigeons

Separate groups of pigeons were trained to perform symbolic delayed matching to sample with auditory and visual sample stimuli. For animals in the auditory group, ambient tones that varied in frequency served as sample stimuli; for animals in the visual group, ambient red and green lights served as sample stimuli. In both cases, the sample stimuli were mapped onto the yellow and blue comparison stimuli presented on left and right pecking keys. In Experiments 1 and 2, it was found that visual and auditory delayed matching were affected in the same ways by several temporal variables: delay, length of exposure to the sample stimulus, and intertrial interval. In Experiments 3, 4A, and 4B, a houselight presented during the delay interval strongly interfered with retention in both visual and auditory groups, but white noise presented during the delay had little effect in either group. These results seem to be more in line with a prospective memory model, in which visual and auditory sample stimuli are coded into the same instructional memories, than with a model based on concepts of retrospective memory and modality specificity.     

In the dark II: spatial choice when access to extrinsic spatial cues is eliminated

Rats were tested in a specially constructed radial-arm maze that eliminated access to extramaze visual cues and allowed any effects of intramaze cues to be controlled. Despite this, choice accuracy was controlled by the spatial location of previously visited arms. Part of this control was attributed to vestibular or kinesthetic cues. This conclusion was corroborated by the finding that when explicit visual cues were moved from their standard (trained) spatial locations to novel locations, control of spatial choices was completely disrupted. The latter finding indicates that cues intrinsic to the rat (kinesthetic or vestibular information) and cues extrinsic to the rat (visual stimuli) operate in an integrated fashion.     

Effects of varying trial distribution,intra- and extramaze cues,and amount of reward on proactive interference in the radial maze

Rats are typically less accurate in their arm selections in the radial maze over successive trials in a session (Roberts & Dale, 1981). In the present study, rats’ choice accuracy declined when such trials were separated by 2-min (massed) but not by 2-h (spaced) intertriai intervals. Changing intramaze visual/tactile arm stimuli (Experiments 1 and 3) or extramaze landmark stimuli (Experiment 4) between trials weakened the massed-trials effect, but changing the number of food pellets per arm, either alone or in conjunction with changes in intramaze cues (Experiments 2 and 3), did not. The rats also tended to avoid the spatial locations of their last four choices on a previous trial during their first four choices on a current trial, and more so with massed than with spaced trials. These findings indicate that intertriai proactive interference (PI) occurred only with massed trials and was weakened by changing intra- and extramaze cues between such trials.     

The role of test stimuli in matching to compound samples by pigeons

Two pigeons matched to sample in a three-key operant conditioning chamber. In Experiment I, two different kinds of samples were presented on the center key.Element samples were members of one of two sample sets — colors (a red or blue disk) or lines (a vertical or horizontal orientation of a set of white lines). These samples were followed by their respective sample sets on the side keys as comparison stimuli.Compound samples consisted of a set of lines superimposed on a colored disk. Following these samples, either sample set could appear as comparison stimuli. Matching to compound samples was less accurate than matching to element samples. One interpretation is that sharing of attention among elements of a compound sample weakened stimulus control by each element. A different interpretation is that an element sample controlled matching better because it was physically identical to a comparison stimulus whereas a compound sample was not. Experiments II–IV evaluated this “generalization decrement” alternative by testing element- vs. compound sample control with both element and compound comparison stimuli. Irrelevant elements were added to form compound comparison stimuli, some of which were physically identical to a preceding compound sample, but never identical to an element sample. In all experiments, the addition of irrelevant elements of comparison stimuli reduced sample control. However, the generalization decrement hypothesis failed to predict how differences in performance maintained by element and compound samples were affected by different tests of sample control. Matching accuracy appeared to be independently determined by the number of elements in a sample and whether irrelevant elements were present during tests of sample control.     

Transfer of oddity learning in the pigeon

Two pigeons were trained on a six-key modified oddity-from-sample procedure. The stimuli were olor pictures of birds, butterflies, and human faces. Initially, the third peck on the sample key which presented one of three different bird pictures) lit only one comparison key. Every three dditional pecks on the sample illuminated another comparison key. Fifteen sample pecks produced he maximum of five comparison stimuli. A peck on the comparison key that presented the non-atching bird picture produced grain. Pecks on matching keys turned off all the comparison keys nd repeated the trial. The birds learned to peck each sample until the non-matching comparison timulus was produced, and then to peck that key. After acquisition (70%–90% accuracy), the hree bird stimuli were replaced by a new set of three bird pictures. Subsequent phases provided ew sets of bird, butterfly, and human face stimuli. Both birds showed transfer of oddity learning o the novel samples. The data suggest that the birds may have been engaging in conceptual-type oddity learning, rather than learning discrete five-key discriminations or a series of two component chains.     

No evidence for overshadowing or facilitation of spatial pattern learning by visual cues

Two experiments were conducted to examine the effects of redundant and relevant visual cues on spatial pattern learning. Rats searched for hidden food items on the tops of poles that formed a square (Experiment 1) or a checkerboard (Experiment 2) pattern. The experimental groups were trained with visual cues that specified the locations of the baited poles. All groups were tested without visual cues so that any overshadowing or facilitation of spatial pattern learning by visual cues could be detected. Spatial choices were controlled by the spatial pattern and by the visual cues in both experiments. However, there was no evidence of overshadowing or facilitation of spatial pattern learning by visual cues in either experiment. The results are consistent with the idea that the representation of the spatial pattern that guides choices is not controlled by the same learning processes as those that produce associations between visual cues and food locations.     

Directed forgetting in monkeys

Based on several recent demonstrations of a directed forgetting effect in pigeons, three experiments were carried out in an attempt to demonstrate directed forgetting in three squirrel monkeys. During initial training with a delayed matching-to-sample procedure, retention tests were always given for sample stimuli followed by remember cues (R-cues) and were always omitted for sample stimuli followed by forget cues (F-cues). Retention of F-cued items was tested on probe trials after initial training. The first two experiments examined the effects of R- and F-cues on memory for slide-projected pictures, with different pictures used on each trial of a session. In Experiment 1, a complex design was used in which one or two sample pictures were presented on each trial; when two pictures were presented, both could be R-cued or F-cued, or one could be R-cued and the other F-cued. A simpler design was used in Experiment 2, with only single pictures presented as sample stimuli and half the trials within a session R-cued and the other half F-cued. In both of these experiments, no differential retention of R- and F-cued stimuli was found, even at a retention interval as long as 16 sec. In Experiment 3, a series of studies was performed to test for directed forgetting when only two sample stimuli were used repeatedly throughout training and testing. With two pictures as sample stimuli, clear evidence of directed forgetting was found in Experiment 3b. It is suggested that the directed forgetting effect may arise only when a small set of sample stimuli is used.     

Stimulus stringing by pigeons: Conditional strings

Pigeons were trained to produce one serial list in the presence of a green background cue and another serial list in the presence of a red background cue when the items for both serial lists were presented on each trial. This demonstrated a combination of serial learning and conditional discrimination learning not previously shown in pigeons. Specifically, when presented with four geometric forms, A B C D, in random locations of a five-key display, the pigeons learned to peck A B C when the background was green and A B D when the background was red. Accuracy on the conditional string ranged from 73% to 85%. Transfer tests using different locations of the stimuli on the keys showed positive transfer, thus ruling out learning of specific locations as the basis of the accurate performance. Above-chance performance was maintained when the conditional colors were presented only on the key that did not contain one of the serial stimuli. The results are interpreted in terms of a chaining model that postulates that the sequential selections were controlled by cues produced by both onset of the trial and prior selections within the trial.     

Extinction of stimulus elements decreases the rate of conditional discrimination learning

Pigeons were trained on a successive discrete-trial conditional discrimination, in which either of two colors appeared on the center key and either of two forms appeared on the two side keys. Some combinations of color and form (S+ trials) were followed by food; other combinations (S-trials) were followed by no food. The colors on the center key appeared throughout the intertrial interval (ITI) preceding the trial period in which both the color and the form compound were presented or the color appeared only during the trial period in compound with the forms. Presentation of the colors during the ITI substantially degraded acquisition of two separate types of conditional discrimination. The results show that the temporal correlation of the eolors-with food, independent of their association with the form cues, played a substantial role in determining their availability for acquisition of the conditional discrimination.     

Sustained attention: Stimulus control determined by schedule of cue production interacting with cue duration

In a study of sustained attention (“vigilance”), pigeons performed a conditional discrimination in a 3-key operant chamber. Pecking a white center key initiated a 0.2- or 2.0-sec cue (a red or green disk). The side keys then displayed white disks, and a peck on the right or left key was reinforced depending on whether the preceding cue was red or green. Pecks on the white center key initiated the cue according to one of two schedules of cue production (FR 1 or VI 7.5 sec). Control of side key choices by 0.2-sec cues was disturbed by transition from FR 1 to VI 7.5, and recovered after the schedule of cue production changed from VI 7.5 back to FR 1. Control of choices by 2.0-sec cues was not affected by changing schedules of cue production. Rates of pecking the cue were higher than rates of cue-producing responses.     

Interference of delayed matching to sample in pigeons: Effects of interpolation at different periods within a trial and stimulus similarity

Delayed matching-to-sample performance by pigeons was interfered with by displaying a monochromatic annulus around the center (sample) pecking key. The wavelength of the annulus and its point of interpolation within a trial were varied to determine possible differential effects on matching accuracy. Experiment 1 showed that delayed matching was most disrupted when the interference stimulus (570 nm, 630 nm, or achromatic white) appeared during the delay interval of a trial. Little if any disruption occurred when the interference stimulus was present during the sample and choice periods. The spectral relationship between the chromatic interference stimuli (570 and 630 nm) and the sample stimuli (570 and 630 nm) did not consistently influence the degree to which matching accuracy was affected in any interpolation condition. Experiment 2 found a similar pattern of within-trial effects when the interference stimulus was simply a change from a white achromatic annulus to a chromatic one. This finding indicates that illumination changes, such as the popular houselight variation, are not necessary to produce interference in delayed matching to sample. Even with illumination held constant, however, performance was not differentially sensitive to the similarity between interference and sample stimulus wavelengths. It is suggested that other experiments showing similarity effects in interference of delayed matching to sample were conducted in such a way that subjects confused the interfering stimuli with the samples.     

Discrimination and representation of relative numerosity in a bisection task by pigeons

We trained 4 pigeons in a numerical bisection task to discriminate between pairs of keylight flashes with a ratio of 1∶3 (2 vs. 6, 4 vs. 12, and 8 vs. 24) that were presented in a sample phase. Responses to the blue key were reinforced after a sequence of a larger number of flashes, and responses to the white key were reinforced after a sequence of a smaller number of flashes. The intervals between flashes in the sample phase were randomized to attenuate the covariation of temporal cues with flash number. Pigeons responded accurately in each of the discriminations, with typically 85%–90% correct responses. Transfer tests showed that the proportion of large responses increased with number and performance generalized to larger values outside the training ranges. Psychometric functions superposed when plotted on a relative scale, and estimates of Weber fractions were approximately constant, suggesting that variability was scalar. However, contrary to previous research in nonhumans, bisection points were located at the arithmetic, not geometric, mean. Hierarchical logistic regressions confirmed significant control over responding by number beyond that attributable to temporal cues. These results show that pigeons are able to respond accurately in a relative numerosity discrimination with successively presented visual stimuli, although the nature of the numerical representation and response rule remains unclear.     

Spatial selective attention and asynchrony of cognitive systems in adult dyslexic readers: an ERPs and behavioral study

The aim of this study was to gain additional knowledge about the asynchrony phenomenon in developmental dyslexia, especially when spatial selective attention is manipulated. Adults with developmental dyslexia and non-impaired readers underwent two experimental tasks, one including alphabetic stimuli (pre-lexical consonant–vowel syllables) and the other containing non-alphabetic stimuli (pictures and sounds of animals). Participants were instructed to attend to the right or left hemifields and to respond to all stimuli on that hemifield. Behavioral parameters and event-related potentials were recorded. The main finding was that the dyslexic readers demonstrated asynchrony between the auditory and visual modalities when alphabetic stimuli were presented on the right hemifield. These results suggest that intact reading is linked to a synchronized auditory and visual speed of processing even when spatial selective attention is manipulated. The findings of the current study are discussed in terms of asynchrony between modalities as a neurocognitive marker in developmental dyslexia.     

Symbolic,identity, and probe delayed matching of sounds by the bottlenosed dolphin

The short-term memory for sounds of the bottlenosed dolphin was tested using symbolic, identity, and probe forms of the delayed matching-to-sample (DMS) task. The forms differed in the number (one or two) or nature (symbolic or identity matches of sample sounds) of postdelay test stimuli available as memory retrieval cues. Although symbolic DMS was difficult to learn, the final performance level was approximately equal to that for identity or probe DMS. On all tasks, the dolphin’s responses were above 80% correct through to delays of 90 sec and, in some cases, through to delays of 180 and 240 sec, the “limits” being governed mainly by the dolphin’s reluctance to continue being tested at long delays. Encoding of sample stimuli into their learned symbolic representation was hypothesized to have reduced symbolic DMS to a recognition memory task, resulting in the observed equivalence of performance with the other two recognition memory tasks. The probe DMS results, unlike those for identity or symbolic DMS, showed no significant proactive interference effects from samples of prior trials. Instead, proactive interference was traceable to the probe value of the prior trial. Overall, the auditory DMS data for the dolphin were functionally similar to results reported for monkeys tested on symbolic, identity, and probe visual DMS tasks.     

Behavioral contrast and type of reward: Role of elicited response topography

Groups of pigeons were exposed to multiple variable-interval variable-interval and multiple variable-interval extinction schedules of either food or water reinforcement for keypecking. Discriminative stimuli associated with component schedules were located either on the operant key or on a second “signal” key. When the stimuli were projected on the operant key, positive contrast appeared during discrimination conditions with either food or water as the reinforcer. When the stimuli were projected on the signal key, overall responding to the operant and signal keys showed contrast with food, but negative induction with water as the reinforcer. In the latter condition, the signal for the variable-interval shcedule of water reinforcement elicited a variety of water-related behavior, only some of which was directed at the signal. Thus, the type of reward and location of discriminative stimuli interacted to determine the presence or absence of behavioral contrast effects. In large part, these results support and extend the autoshaping view of contrast.     

Attenuation by contextual cues of retroactive interference of a conditional discrimination in rats

We investigated the effect of associating unique contextual cues with an interpolated learning task on retroactive interference in long-term memory. Rats were originally trained in a two-bar operant chamber with an auditory conditional discrimination stimulus. During interpolated learning, which occurred in either the original or a new context, some rats were trained on a probability learning task that did not include the auditory stimuli present during original learning. Subsequent retraining on the original conditional discrimination task in the original context showed that (1) significant retroactive interference occurs in rats, and (2) the presence of unique contextual cues during interpolated learning significantly reduces this interference. These results extend the conditions under which the susceptibility to retroactive interference can be altered by contextual cues.     

In the dark: Spatial choice when access to spatial cues is restricted

The cognitive mechanisms involved in spatial choice when access to visual cues is restricted were examined in three experiments using male rats. A specially constructed radial-arm maze was used, in which extramaze visual cues could not be perceived from the central arena, but could be perceived from the maze arms. Choices were very accurate when the maze was not rotated during each trial, but inaccurate when the maze was rotated. This suggests that intramaze cues were involved in the control of choices. However, the data clearly showed that choices were not simply controlled by intramaze cues. Rather, control by intramaze cues interacted in a more complex manner with representations of the spatial locations of goals. Such spatial representations were involved in the control of choice despite the absence of visual spatial cues at the time choices were made.     

Differential outcome expectancies and directed forgetting effects in pigeons

Pigeons were trained in a two-choice delayed matching-to-sample task with red and green hues. A brief postsample cue (a vertical or horizontal line) signaled whether the comparison stimuli would be presented or omitted on each trial. Comparison stimuli were always presented following the remember (R) cue, but never following the forget (F) cue or no-cue trials. One group of birds, the differential outcome (DO) group, received reinforcement with a probability of 1.0 for correct responses following one sample stimulus and a probability of 0.2 for correct responses following the other sample stimulus. The nondifferential outcome (NDO) group received reinforcement with a probability of 0.6 for correct responses to either stimulus. The effect of postsample cues was greater for the DO group than for the NDO group. Relative to the NDO group, the DO group displayed higher accuracy on R-cue trials and lower accuracy on F- and no-cue trials. Both tendencies contributed to the enhanced cue effectiveness obtained in the DO group. The results indicate that outcome expectancies are subject to maintenance rehearsal, which comes under the control of postsample R and F cues. They also suggest that maintenance rehearsal may be easier to sustain under DO conditions than under NDO conditions when a memory test is anticipated, but that it may be easier to terminate maintenance rehearsal under DO conditions when a memory test is not anticipated. The results are inconsistent with the assumption that the rehearsal of outcome expectancies is automatic.