Categorical discrimination of objects and pictures by pigeons

With a three-choice instrumental discrimination procedure, pigeons were taught to distinguish small spherical objects from nonspherical objects. Spherical objects were defined as positive, nonspherical objects as negative. A device allowing an automatic presentation of the stimuli was employed. The subjects actually pecked the objects, and grain rewards were presented directly beside the correct objects. Acquisition was rapid, with the birds reaching a criterion of 80% correct choices within less than 150 trials. There was evidence that more than 200 objects were remembered individually over 3 months. Pigeons transferred the discrimination of spherical/nonspherical objects to novel objects. The criteria by which the birds judged the sphericity of objects seemed to be similar to those applied by humans. They could apply the categorization in a relational manner and generalize it to apply to photographs and drawings of objects. The categorization competence was retained for at least 3 months.     

The nature of discrimination learning in pigeons

The results from five experiments are considered in relation to two of Spence's (1937, 1938) proposals concerning discrimination learning. In Experiments 1 and 2, we investigated whether his ideas about the interaction between excitatory and inhibitory generalization gradients can be used to understand how animals solve a complex patterning discrimination. The results supported a development of his proposals as put forward by Pearce (1994), provided a modification was made to Pearce's rulefor determining the shape ofthe generalization gradient. In Experiments 3, 4, and 5, we examined whether animals would pay more attention to stimuli that are relevant, rather than irrelevant, to the solution of a discrimination. The results supported this proposal for stimuli comprising visual patterns, but not for those comprising plain colors. The results also indicated that change of attention was a consequence of preliminary receptor-exposure acts, as envisaged by Spence, and not of more central changes in attention.     

Time-of-day discrimination by pigeons,Columba livia

Pigeons were trained to discriminate between four keys. One provided food in the mornings, another provided food in the afternoons, and two never provided food. Three experiments were performed to determine whether pigeons could track food availability over a 24-h period. All the subjects appeared to demonstrate time-place associative learning. A fourth experiment was designed to investigate the mechanisms underlying the timing behavior. Lights-on time was shifted back by 6 h, and no decrease in performance was found during the first session following the phase shift. This suggests that a circadian type of timing mechanism with a self-sustaining oscillator mediates time-place learning over a period of 24 h. Further support for this notion was found in a fifth experiment, in which the subjects were tested in constant dim light. In that experiment, the subjects’ continued correct responding provides additional support for a self-sustaining circadian timer.     

Conditioned inhibition in feature negative discrimination learning with pigeons

Discrimination performance was investigated with pigeons using feature negative (FN) discrimination procedures which differed in the temporal arrangement of the stimuli on S? trials. In both procedures, a single common element was presented on reinforced (S+) trials. In thesimultaneous FN procedure, a distinguishing element was presented simultaneously with the common element of S? trials. In thesequential FN procedure, the distinguishing element preceded onset of the common element on S? trials. In two experiments, the sequential FN procedure yielded better discrimination performance. In Experiment 1, a summation test designed to separate learning and performance variables indicated that sequential FN subjects had learned the negative relationship between the distinguishing element and reinforcement while simultaneous FN subjects had not. In Experiment 2, summation and acquisition tests indicated that the distinguishing element developed inhibitory properties in the sequential FN procedure but not in the simultaneous FN procedure.     

Scalar effects in the visual discrimination of numerosity by pigeons

Pigeons trained in a conditional discrimination procedure to respond to a visual array made a left or right choice, depending on which of two numbers of elements (i.e., anchor numerosities) the array contained. They were then tested with novel arrays at these anchor numerosities, as well as at interpolated and extrapolated numerosities. Various control conditions showed that the birds’ discrimination performance was primarily based on stimulus numerosity, and not on other factors, such as brightness or area. Results from a series of tests, spanning a wide range of numerosities, conformed to scalar principles. Psychometric functions showed superposition, indicating that Weber’s law applies to numerosity discrimination. The subjective midpoint between anchor values was at the geometric mean. Variability about this bisection point increased in proportion to the numerical value of the mean.     

Attempts to demonstrate magnetic discrimination by homing pigeons in flight

Eight homing pigeons, trained to fly between two elevated feeders within a flight tunnel, were tested for their ability to discriminate between two magnetic field stimuli and two acoustic stimuli, using a unitary discrete-trials procedure with successive presentation of stimuli. Magnetic stimuli consisted of the ambient magnetic field and a reduced magnetic field in which the vertical component of the field was reduced to 50% of its ambient value. Acoustic stimuli consisted of an ambient white noise and the white noise plus a tone. Stimuli were paired with food reward and either a time penalty (Experiment 1) or electric shock (Experiment 2). Although subjects could discriminate sounds with our procedures, none of the subjects demonstrated discrimination of magnetic fields. The failure of pigeons to discriminate magnetic stimuli is discussed as a consequence of either the failure to provide conditions sufficient for such discrimination or the absence of a magnetic sense in these animals.     

Expectancies as mediators in the differential-reward conditional discrimination performance of pigeons

In a series of within-subject experiments employing a two-choice delayed conditional discrimination task, pigeons chose correctly more often when kind of correct choice and kind of reinforcer were perfectly correlated than when uncorrelated. Correct choice behavior fell to chance levels when the correlation was reversed or when it was removed by using only one kind of reinforcer. Implications for mediation theories are discussed, with the conclusion being that, although the possibility that instrumental mediators are present in this situation cannot be dismissed, the overall pattern of results indicates that classical mediators are of principal importance in this type of task.     

Mother-child conversations about pictures and objects: referring to categories and individuals

The distinction between individuals (e.g., Rin-Tin-Tin) and categories (e.g., dogs) is fundamental in human thought. Two studies examined factors that influence when 2- to 3-year-old children and adults focus on individuals versus categories. Mother-child dyads were presented with pictures and toys (e.g., a picture of a boat or a toy boat). Conversations were coded for references to generic categories ("Dogs are furry"), ostensive labels ("This is a dog"), or specific individuals ("Lassie"). Overall, pictures generated more talk about categories; objects generated more talk about individuals. However, when objects could not be manipulated, speakers expressed relatively more category references. These results suggest that representations (in the form of pictures or objects-on-display) encourage young children and parents alike to think about categories.     

Visual discrimination learning and memory in nocturnal prosimians

The ability of two nocturnal prosimians—greater galago and slow loris—to learn and to remember two-dimensional black-white pattern discriminations was investigated. There was no significant species difference. Both were found to be: sensitive to the number of visual cues available, able to benefit from repeated exposure to similar problems, capable of retaining previously learned material over a long period of time. Although they are individually quite variable in performance, these primitive primates are by no means untrainable on visual discrimination problems, as previous reports have suggested.     

Simultaneous discrimination reversal learning in pigeons and humans: anticipatory and perseverative errors

Pigeons were trained on a two-choice simultaneous discrimination (red vs. green) that reversed midway through each session. After considerable training, they consistently made both anticipatory errors prior to the reversal and perseverative errors after the reversal, suggesting that time (or number of trials) into the session served as a cue for reversal. In Experiment 2, to discourage the use of time as a cue, we varied the location of the reversal point within the session such that it occurred semirandomly after Trial 10, 25, 40, 55, or 70. Pigeons still tended both to anticipate and to perseverate. In Experiment 3, we required 20 pecks to a stimulus on each trial to facilitate memory for the preceding response and sensitivity to local reinforcement contingencies, but the results were similar to those of Experiment 2. We then tested humans on a similar task with a constant (Experiment 4) or variable (Experiment 5) reversal location. When the reversal occurred consistently at the midpoint of the session, humans, like pigeons, showed a tendency to anticipate the reversal; however, they did not show perseverative errors. When the reversal location varied between sessions, unlike pigeons, humans adopted a win–stay/lose–shift strategy, making only a single error on the first trial of the reversal.     

Interocular transfer in pigeons of color discrimination but not motor response training

Adult pigeons with one eye covered were trained to peck a response key using grain as a reinforcer. In subsequent tests, with the trained eye covered and the control eye open, the birds failed to peck the key. The subjects were then divided into two groups for a second experiment. The first group was trained on a single-key, peck/no-peck color discrimination task with the original control eye covered. When tested for interocular transfer of discrimination performance, these birds failed to respond at all. They were then trained to peck a blank response key with the training eye covered and the control eye open. Control-eye tests after this motor response training resulted in excellent transfer of color discrimination performance. The second group of subjects was trained to peck a blank key with first one eye covered and then the other, before monocular discrimination training was begun. These birds showed excellent transfer of discrimination performance during control-eye tests. These results show that, at least in the operant paradigm, motor response training does not transfer interocularly and this lack of transfer may interfere with transfer of discrimination performance.     

Imaginary pictures,real life stories: the FotoDialogo method

This paper explores methodological issues of recording, revisiting and portraying women’s life experiences and their connections to the past, to their families and to their communities. It examines the personal histories and collective memories of a group of low‐income Hispanic women, through the application of an innovative research tool that uses pictures and storytelling as projective techniques. The FotoDialogo Method uses a set of original drawings to initiate dialogical interviews, to inspire research participants to tell their stories, and to critically analyze the situations presented in these stories. The research study took place at a community‐based organization providing non‐formal education programs to the Spanish‐speaking population in a US inner‐city setting. The FotoDialogo Method has the potential to be an effective tool to help underprivileged women break the silence concerning their experiences of oppression and to engage them in a process of self‐discovery and transformation that empowers them to become change agents within their families and communities.     

Enhancement of pigeons’ conditional discrimination performance by expectancies of reinforcement and nonreinforcement

Prior work has shown that when the separate correct responses of a conditional discrimination are followed by different reinforcing outcomes, performance is enhanced relative to that obtained under the conventional, single-reinforcer procedure. Four experiments with pigeons yielded the analogous finding when the different outcomes were reinforcement and explicit nonreinforcement. Controls indicated that the results could not be attributed to the effects of intermittent reinforcement, to possible differences in cue duration, or to a variety of potential sources of conditioned reinforcement. An interpretation in terms of expectancy learning is proposed.     

Reinstatement of postresponse stimuli prior to reward in delayed-reward discrimination learning by pigeons

Delayed-reward learning in pigeons was examined using a simultaneous red-green visual discrimination task in which the conditions during the delay interval were varied between groups. The nondifferential group received training in which the stimulus present during the 1-min delay was the same following a peck on the correct and incorrect colors. The other three groups received 1-min delay training in which different stimuli occurred in the delay interval following correct and incorrect choices. The differential group received continuous, differential stimuli during the delay. The reinstatement group received the differential stimuli in the 10 sec immediately following the choice and during the last 10 sec of the delay. The reversedcue group was treated in the same way, except that the 10-sec delay stimulus immediately following an incorrect response was also presented for 10 sec prior to reward on correct choices, and the stimulus following a correct response also occurred 10 sec before nonreward on incorrect choices. Nondifferential birds failed to learn the discrimination, while differential and reinstatement birds learned it readily. The reversed-cue birds learned to choose the incorrect stimulus. Differential and reinstatement birds showed no decrement in performance when the delay was increased to 2 min. These findings suggest that similarity of prereward and postresponse delay stimuli controls choice responding in long-delay learning, a finding compatible with both memorial and conditioned reinforcement interpretations.     

Coding of feature and no-feature events by pigeons performing a delayed conditional discrimination

Pigeons’ performance of a delayed conditional discrimination with presence versus absence of conditional (sample) stimuli was examined in two experiments. The pigeons showed steeper retention functions with feature (i.e., presence) samples (either food or yellow) than with no-feature (i.e., absence) samples (either no food or no yellow). These results suggest that pigeons code features and respond only by default to test stimuli (comparisons) associated with no features. In contrast, the overall superiority of performance on no-feature-sample trials compared with feature-sample trials in both the food/no-food- and yellow/no-yellow-sample tasks was reversed at a 0-sec delay in the food/no-food-sample group, but not in the yellow/non-yellow-sample group. This difference in results with hedonic versus nonhedonic samples suggests that the crossover in delay performance on food/no-food-sample trials is produced by the formation of backward associations between the food-associated comparison stimulus and the food sample.     

Elemental versus configural perception in a people-present/people-absent discrimination task by pigeons

In the present experiment, we investigated whether pigeons rely exclusively on elemental information or whether they are also able to exploit configural information in apeople-present/people-absent discrimination task. Six pigeons were trained in a go/no-go procedure to discriminate between 800 color photographs characterized by the presence or absence of people. Thepeople-present stimuli were designated as positive, and thepeople-absent stimuli were designated as negative. After training and a subsequent generalization test, the pigeons were presented with both familiar and novel people-present stimuli containing human figures that were distorted in one of seven different ways. All the pigeons learned the initial discrimination and also showed generalization to novel stimuli. In the subsequent test, performance on all types of distorted stimuli was diminished in comparison with that on the intact original pictures from which they had been derived. At the same time, however, peck rates clearly exceeded the level of responding found for regular people-absent stimuli. This result strongly suggests that responding was controlled by both the constituting target components and their spatial relations and, therefore, points to the dual importance of elemental and configural information.     

Visual processing of pictures and letters in alphabet books and the implications for letter learning

Alphabet books as studied in this research typically highlight one letter per page combined with a depiction of a word that begins with the letter (e.g., a bear illustrates B). This study tests whether children’s letter knowledge improves as a result of alphabet book sharing and how the visual processing of pictures and letters affects learning from repeated alphabet book readings. The study is designed as a randomized control trial in which participants were assigned to one of two experimental groups (N = 30) or a control group (N = 15). Half of the experimental group received version A in which the letters A–L were illustrated with anthropomorphic figures and the letters M–Z with objects. Half received version B in which the letters A–L were illustrated with objects and the letters M–Z with anthropomorphic figures. Mean age of the children was 57.6 months (SD = 3.6). While sharing the alphabet book we registered children’s eye movements in the first and fourth (last) reading session. Alphabet book reading stimulated letter knowledge although the make-up of the alphabet book moderated the effects. Relatively more visual attention to pictures of anthropomorphic figures interfered with learning letters from alphabet book sharing. Visual attention to letters also predicted letter knowledge and learning. Only a small part of each letter attracted children’s attention and the briefer their fixations on this distinctive area, the more letters they knew at the pretest and were able to learn from alphabet book sharing.     

Transposition in pigeons: reassessing spence (1937) with multiple discrimination training

We studied transposition in pigeons, using multiple-pair discrimination training. Four birds discriminated two pairs of circles: 1+ 2− and 5+ 6− or 1− 2+ and 5− 6+ (digits denote circle diameters and plus and minus signs denote reward and nonreward, respectively). Four other birds discriminated four pairs of circles: 1+2−, 1+3−, 4+6−, and 5+6−or 1−2+, 1−3+, 4−6+, and 5−6+. Finally, 4 birds discriminated only one pair of circles: 1+ 2−, 1+ 2−, 5+ 6−, or 5− 6+. Testing included five new pairs—1/5, 2/3, 2/6, 3/4, and 4/5—that distinguished absolute from relational accounts of transposition. The pigeons’ relational responding rose from one- to two- to four-pair training. The similarity of the testing stimuli to one another also affected relational responding: Transposition increased with highly dissimilar stimuli. Neither Spence’s (1937) theory nor existing relational accounts could predict the obtained pattern of relational responding.