Visual effects of opiates in pigeons. III. Luminance and wavelength sensitivity.

In a psychophysical task that permitted dissociations among sensitivity, overall stimulus control, and bias, pigeons learned to discriminate among stimuli along separate wavelength and luminance dimensions. Subsequent tests followed injections of morphine (1-8 mg/kg) and morphine plus naloxone (3 mg/kg). Morphine decreased sensitivity to both dimensions, and reduced overall control by luminance. These effects were reduced or reversed by naloxone. Morphine's effects appeared more pronounced for luminance than for wavelength stimuli. There were no consistent drug effects on response bias.

Selective attention and search images in pigeons.

In a visual search task, pigeons detected targets when pretrial visual cues or blocked trial sequences signaled the target's identity. Sequential priming was robust over a wide range of intertrial intervals, but visual priming was unstable when the delay between cue offset and display onset was varied. Larger target set sizes enhanced sequential, but not visual, priming. Sequential priming did not depend on display size over the range of relatively large displays used. However, ambiguously cued targets in small displays were detected more quickly than primed targets in large displays. These findings suggest that naturalistic selection biases, or "search images," may be attributable to sequential priming and that the common attentional mechanism has moderately selective properties.

Attentional priming and visual search in pigeons.

Advance information about a target's identity improved visual search efficiency in pigeons. Experiments 1 and 2 compared information supplied by visual cues with information supplied by trial sequences. Reaction times (RTs) were lower when visual cues signaled a single target rather than two. RTs were (Experiment 1) or accuracy improved (Experiment 2) when a sequence of trials presented a single target rather than a mixture of 2. Experiments 3, 4, and 5 considered the selectivity of visual priming by introducing probe trials that reversed the usual cue-target relationship. RT was higher following such miscues than following the usual 1- or 2- target cuing relationships (Experiment 3); the miscuing effect persisted over variations in the target's concealment (Experiments 4 and 5), but did not occur when the target was presented alone (Experiment 4). The findings indicate that priming modifies an attentional mechanism and suggest that this effect accounts for search images.

Visual effects of opiates in pigeons: I. Target location in visual search.

Pigeons pecked at target forms, located in arrays of distractors. In experiment 1 the number of distractors and their similarity to the target varied. In experiment 2, similarity was varied over a more extended range. Drug tests used morphine in doses ranging from 1 to 6 mg/kg, naloxone (0.3-3 mg/kg) alone and combined with morphine. Morphine had relatively small effects on accuracy; however, it produced pronounced elevations in reaction time. Significant interactions with display variables indicated a visual component to the morphine effect. Naloxone alone had no effect; naloxone combined with morphine blocked the morphine effect.

Visual effects of opiates in pigeons: II. Contrast sensitivity to sinewave gratings.

In a simultaneous forced-choice procedure, three pigeons learned to discriminate between a blank field and sinewave gratings of equal space-averaged luminance. Conditions included two spatial frequencies and, for each, a series of contrasts, which were varied over a range sufficient to generate psychometric functions. Drug tests used two doses of morphine and a condition that combined naloxone with the higher dose. Morphine decreased contrast sensitivity, although this outcome was reliable only at the higher dose and the higher spatial frequency. This effect was reduced and usually blocked by naloxone. Morphine-induced changes in pupil size were too small to account for the opiate effect.

Sequential effects in dimensional contrast.

Two experiments examined pigeons' response rates during short trials signaled by stimuli closely spaced along a wavelength continuum. In Experiment 1 separate halves of the continuum were correlated with different reinforcement schedules. In Experiment 2, the middle stimulus was accompanied by a lower probability of reinforcement than were the remaining wavelengths. Both procedures resulted in dimensional contrast "shoulders," seen as relatively enhanced or depressed response rates in the presence of stimuli between the extreme of the continuum and the border separating the positive and negative stimuli. Sequential analyses addressed possible contributions of the following interactions: (a) local contrast, seen when rate during a given schedule depends on the schedule in the just-preceding trial; (b) modification of local contrast by the similarity of the signaling stimuli (P. Blough, 1983); and (c) schedule-independent rate contrast, seen when rate in a given trial depends on the rate controlled by the stimulus that accompanied the just-preceding trial (Malone & Rowe, 1981). Dimensional contrast functions were similar when isolated according to the schedule, to the similarity of the signaling stimulus, and to the response rate of the just-preceding trial. The interactions noted above do not appear to make important contributions to this effect.

Local contrast in multiple schedules: the effect of stimulus discriminability.

A three-ply multiple schedule assessed responding in a standard component as a function of the just-preceding schedule. The principal experimental condition was the difference among the wavelengths signaling the schedule components. Only the pigeons working in a narrow wavelength range showed persistent positive local contrast; that is, response rate during the standard component was higher when that component followed extinction than when it followed itself. Birds in both narrow- and medium-range groups showed persistent negative local contrast; that is, rate was lower following a relatively rich component. The dissipation of positive contrast appeared to be most clearly related to the establishment of differential responding. Negative contrast was inversely related to wavelength differences. Theories pertaining to contrast must account for the role of discrimination in both positive and negative types.

Psychophysical assessment of visual dysfunction.

Selected psychophysical techniques for nonhuman animals are described. These include operant learning methods and a new reflexive technique that may prove especially efficient. Problems of particular interest for toxicological research include control of the physical stimulus, choice of species, separation of stimulus from attentional effects, response bias, and pre- and post-training efficiency.

The pigeon's distant visual acuity as a function of viewing angle.

Distant visual acuity was determined for several viewing angles in two restrained White Carneaux pigeons. The behavioral technique was a classical conditioning procedure that paired presentation of sinusoidal gratings with shock. A conditioned heart rate acceleration during the grating presentation indicated resolution of the grating. The bird's acuity was fairly uniform across a large range of their lateral visual field; performance decreased slightly for posterior stimulus placement and sharply for frontal placements. The data suggest that foveal viewing is relatively less advantageous for acuity in pigeons than in humans. The data are also consistent with the current view that pigeons are myopic in frontal vision.

Behavioral and dimensional contrast in rats.

Rats pressed a nose key for brain stimulation reinforcement presented on a fixed-interval schedule. Stimuli were drawn at random from a continuum of 12 white noise intensities in the range 62-95 decibels, spaced in 3 decibel steps. Experiment 1 varied the number of stimuli and the reinforcement contingencies associated with them. In Condition I (baseline) all stimuli signaled reinforcement; in Conditions II and III stimuli from one half of the continuum signaled reinforcement and those from the other half, extinction. However, in Condition II the 6 stimuli from the middle of the continuum were omitted. Experiment 2 held constant the number of stimuli and varied their spacing. In Condition I, each of 6 sounds signaled reinforcement. In Conditions II and II, three stimuli from one half of the continuum signaled reinforcement and three from the other half, extinction. However, in Condition II the stimuli were near the extremes of the continuum (Stimuli 1, 3, 4, 9, 10, 12). Condition III replaced Stimulus 3 with Stimulus 6 and Stimulus 10 with Stimulus 7. Behavioral contrast was seen in an increase over baseline in response rate to the stimuli associated with the constant schedule component when the variable component was changed to extinction. Dimensional contrast was seen in a further elevation of rate to intermediate positive stimulus values when stimuli were added to the border region between positive and negative values.

The pigeon's perception of saturation.

Three experiments used similar methods to investigate the pigeon's perception of saturation of monochromatic lights. This trial-wise procedure consisted of brief presentations of positive and negative stimuli in random sequence. Pecks to the positive stimuli were occasionally reinforced on a low fixed-ratio schedule. The first study determined absolute thresholds for "white" and monochromatic lights by establishing a discrimination between lights of various radiances and a dark key. Experiment II investigated generalization from a white light to various monochromatic lights under conditions that minimized the use of luminance as a cue. The third experiment examined discrimination of various monochromatic lights along a colorimetric purity continuum; responses to white light were reinforced, while responses to lights that combined white and monochromatic lights in various proportions were not. The results indicated that lights of different wavelength differ in saturation, but that all are discriminable from white. Wavelengths between 550 and 600 nm are least saturated for the pigeon, and saturation increases markedly as wavelength decreases below this region of the spectrum.

Visual acuity in the pigeon. II. Effects of target distance and retinal lesions.

Visual acuity thresholds for grating targets were determined for three pigeons at target distances ranging from 13 to 73 cm. These measurements were made both while the birds were wearing goggles restricting vision to the frontal field of view and when vision was unrestricted. Using a slightly different method, performance was also compared for target distances of 6 and 13 cm while the goggles were in place. For a second group of three pigeons, acuity data were obtained before and after laser lesions of the retina's foveal region. The findings suggested that acuity was relatively poor for targets at the intermediate distances and that it improved as distance both increased and decreased from these intermediate values. The acuity improvement with increasing distance did not occur, however, when the birds were wearing frontal goggles. The data appear to be consistent with Catania's 1964 suggestion that the pigeon has separate frontal and lateral visual systems that differ in their refractive characteristics. Foveal lesions did not appear to affect acuity for distant targets, and it was concluded that, while the fovea serves the lateral field of view, its presence is not necessary to the static acuity characteristics of this system.

The visual acuity of the pigeon for distant targets.

The acuity of six pigeons was measured in an apparatus that required the birds to make visual discriminations at a distance of 28.75 in. (73 cm) from the stimulus targets. The stimuli were black and white gratings of varying stripe width. A forced choice procedure was used, and both the Method of Constant Stimuli and a descending series technique determined the order of stimulus presentation. Thresholds, obtained by interpolating at the 25% error point on the psychometric functions, ranged from 1.16 to 4.0 min of arc. Thresholds measured in the same apparatus for two human observers were 0.79 and 0.82 min of arc. The descending series design produced lower per cent error rates at the widest stripe value, but otherwise there appeared to be no difference between psychophysical methods. Position preferences occurred in most of the birds; differential per cent error functions and differential latency functions to the two keys illustrate these. Retinal histology revealed shallow, centrally located foveae in the three pigeon breeds used.

The distribution of interresponse times in the pigeon during variable-interval reinforcement.

Three pigeons' pecks were reinforced on 1- and 2-min variable-interval schedules, and frequency distributions of their interresponse times (IRTs) were recorded. The conditional probability that a response would fall into any IRT category was estimated by the interresponse-times-per-opportunity transformation (IRTs/op). The resulting functions were notable chiefly for the relatively low probability of IRTs in the 0.2- to 0.3-sec range; in other respects they varied within and between subjects. The overall level of the curves generally rose over the course of 32 experimental hours, but their shapes changed unsystematically. The shape of the IRT distribution was much the same for VI 1-min and VI 2-min. The variability of these distributions supports the notion that the VI schedule only loosely controls response rate, permitting wide latitude to adventitious effects. There was no systematic evidence that curves changed over sessions to conform to the distribution of reinforcements by IRT.