Green Background Research Articles

Stiles’s π_5 mechanism: failure to show univariance is caused by opponent-channel input

Stiles’s π5 field sensitivity approaches the sensitivity of the long-wavelength (L) cone as the duration of the test flash decreases. Further, for short test flashes mixtures of red and green backgrounds are additive. For long test flashes the backgrounds cancel, the mixture raising threshold less than expected. These results are explained if π5 is approximately the L-cone sensitivity combined with some opponent-channel sensitivity.

Transient desensitization of a red-green opponent site

The threshold for detection of a 3°, 200 msec red test flash may rise immediately after a dim red or green adapting background has been turned off. The threshold falls, however, if the background is yellow; or if the red or green background is slowly flickered during adaptation (e.g. at 2 Hz); or if the test is small and brief (24′, 20 msec). The threshold rise may reflect transient desensitization of a flickersensitive red-green opponent site in the pathway that detects larger and or longer test flashes at low adaptation levels.

Retardation tests of inhibition following discriminative autoshaping

Four experiments explored various applications of the retardation test of inhibition following discriminative autoshaping. In all studies, discriminative autoshaping consisted of food-reinforced presentations of a green key-light CS+ and nonreinforced presentations of a vertical white line on a green background CS−. In Experiment 1, the inhibitory properties of the vertical Une CS− were assessed by comparing the acquisition of keypecking to the now-reinforced vertical line CS in groups previously receiving discriminative autoshaping (as above), discriminative autoshaping with a red key CS−, and nondiscriminative autoshaping. The results indicated that the former CS− was retarded in being transformed into a CS+. In Experiment 2, the discriminative autoshaping procedure was followed by testing for acquisition with independent groups receiving one of four different CSs differentiated by line orientation. The results indicated that the orientation attribute of the CS− was inhibitory, in that a between-subjects resistance-to-reinforcement gradient of inhibition was obtained. In Experiment 3, discriminative autoshaping was followed by a within-subjects resistance-to-reinforcement generalization test based on line orientation, which failed to yield an orderly gradient. The implementation of a DRO contingency in the within-subjects test (Experiment 4) was ineffective in generating an incremental gradient. Implications for inhibitory assessment methodology are discussed.

BRIGHTNESS CONTRAST: A REINTERPRETATION OF COMPOUND CUE AND COMBINED CUE EXPERIMENTS WITH PIGEONS

A group of three pigeons was trained on a 4-ply multiple schedule: a green color and a vertical line superimposed upon an achromatic background as positive stimuli, and a red color and a horizontal line on an achromatic background as negative stimuli. The pigeons were tested with the vertical line superimposed upon different achromatic background intensities, then with the vertical line superimposed upon different green background intensities, and finally with the vertical line and its training achromatic backgfound attenuated (and unattenuated) by a neutral density filter. The gradients peaked at the luminance of the achromatic background used during training and at the equivalent luminance for the green background when it was substituted for the achromatic background. The brightness contrast, not the background luminance, was the critical variable as the neutral density filter attenuated both the line and the background equally, leaving brightness contrast unchanged; there was no response decrement to this attenuated stimulus. Two other groups of three pigeons showed that they attended to line orientation as well as to brightness contrast. The brightness contrast hypothesis was extended to explain results of attention experiments and combined cue experiments which have used line stimuli in combinations with different backgrounds.

Conditional discrimination training and interocular transfer in pigeons

Four groups of pigeons were trained either monocularly or binocularly on a series of successive line orientation discriminations. The role in interocular transfer of both changes in viewing conditions and background cues was examined. Either red or green background illumination to the patterns was used as changes in background cues; whereas alterations in viewing conditions were obtained by transferring from binocular to monocular vision, or from the left to the right eye. The results suggest that the viewing condition can operate in the same way as an external cue does for a conditional discrimination. This finding provides an explanation of the learning of conflicting discriminations with each eye by animals that also show interocular transfer.

Inhibitory effects of omission training

In Experiment 1, pigeons were trained to peck red or blue keys for food reinforcement at variable intervals, while food was contingent on withholding key pecks in the presence of a vertical line (omission training). When the line was briefly superimposed on red or blue in a compound test, responding was reduced. When the orientation of the line was varied during extinction, generalization gradients were variable but often had most responding at or near vertical. In Experiment 2, pigeons were trained in a discrete trials procedure that made food contingent upon pecking in the presence of triangle, and upon the absence of pecking in the presence of red (omission training). Food was never given on green-key trials (extinction). When red or green backgrounds were presented with the triangle in a compound test, responding was reduced similarly in the presence of both key colors. Subsequent resistance to auto-shaping was also similar for red and green. These data, taken together with reports in the literature, suggest that the inhibitory effects of omission training are quite similar to those of extinction. Thus, the crucial condition for obtaining inhibitory effects is not a negative stimulus-reinforcer correlation, as in extinction, but simply the establishment of low rates of responding to the inhibitory stimulus.

AUTOSHAPING WITH COMMON AND DISTINCTIVE STIMULUS ELEMENTS, COMPACT AND DISPERSED ARRAYS1

Four groups of pigeons were trained with a standard autoshaping procedure in which a brief fixed-duration interval always followed by a grain delivery alternated with a longer variable-duration interval never associated with grain delivery. One of two stimuli was always presented during each interval. One of them contained three black dots and a black star on a green background; the other contained four black dots on a green background. The four elements of each stimulus were arranged in a more compact array for two groups and in a more dispersed array for the other two groups. Which of the two stimuli preceded grain delivery was counterbalanced within each pair of groups. The speed of occurrence of the first autoshaped peck was not affected by whether the stimulus containing the distinctive star element preceded grain delivery, but autoshaping was faster when the stimulus arrays were compact than when they were dispersed. During 560 response-independent training trials that followed the first autoshaped peck, this pattern reversed; both discriminative control over responding and the relative frequency of pecking the stimulus that preceded grain delivery were greater for the two groups where this stimulus contained the discriminative element than for the two groups where it contained only common elements. During subsequent testing with stimuli containing only a single element each, the distinctive feature was responded to proportionately more often by the two groups for which it had been an element of the stimulus preceding grain delivery than by the two groups for which it had been an element of the stimulus complex that never was associated with grain delivery. These data add further support to the hypothesis that the initial occurrence of autoshaped responding and its subsequent maintenance are not affected by the same variables. They also suggest that automaintenance is as sensitive as response-dependent training to the presence or absence of a distinctive stimulus element among several common elements and that this sensitivity appears to be independent of the specific method used for presenting the stimuli during automaintenance.

Locust as prey: Factors affecting their vulnerability to predation

Experiments were carried out to investigate four factors which could affect the vulnerability of nymphs of the desert locust, Schistocerca gregaria to predation. Three different vertebrate species of predator were used, humans, lizards, and a chicken. The factors studied were the colour and size/age of the locusts, the background on which the nymphs were presented and the numbers presented (singly or in groups of five). These variables were each found to be important to at least one of the species used, in modifying predation; different variables being important to different predators. The green nymphs surprisingly did not appear to be better protected on the green background than were the yellow and black nymphs.

Relative modulation sensitivities of the red and green color mechanisms

The sensitivities of the human green and red cone mechanisms to sinusiodally flickering light were found to be near equal and independent of field size and estimation method. No wavelength dependency of modulation sensitivity was found. An observer who lacks the red cone pigment (protanope) did not show unusually high flicker sensitivity to green light of 525 nm. The modulation transfer function for the normal observer measured with a green flickering test on a red background is identical to that on a green background when the backgrounds have been equated for the green cones by the protanope. The same is true for the contrast transfer function of the normal observer when determined with a green grating on the red and green backgrounds equated by the protanope.

ATTENTION IN THE PIGEON: A REEVALUATION1

During training sessions, pigeons were successively exposed to compounds consisting of a white triangle on a red background and a white circle on a green background. Key pecking intermittently produced grain reinforcers in the presence of one form-color compound. Once key pecking was confined to the compound associated with reinforcement, the elements-red, green, triangle, and circle-were presented during a test in which no reinforcement was available. Each bird pecked nearly exclusively in the presence of the color previously associated with reinforcement, a result that might be interpreted as indicating that the subjects had attended to color, but not form during training. Pecking was next reinforced when either the triangle or the circle was present. Pecking in the presence of the form previously associated with reinforcement was acquired more rapidly. This result suggests that the birds had learned about the forms during training, and that conclusions about attention based on the lack of differential pecking in the nonreinforcement test may not be appropriate.

Influence of crop background on aphids and other phytophagous insects on Brussels sprouts

SUMMARYMore Brevicoryne brassicae and other alate aphids were caught in yellow water‐traps in a weed‐free crop of Brussels sprouts than in a crop with a weedy background. More B. brassicae colonized Brussels sprout plants in bare soil than in weeds; very few alatae were attracted to cruciferous weeds in the crop. Results in 1 yr suggest that initially larger populations on the weed‐free sprouts became smaller than populations on the weedy sprouts because the larger aphid population attracted more natural enemies. Aleyrodes brassicae and certain Lepidoptera were also more abundant on sprout plants in bare soil than on sprouts surrounded by weeds; more adult A. brassicae were caught in water traps over the bare soil.More A. brassicae were present on sprout plants surrounded by a green than by a brown cloth background but the differences were not significant (P < 0–05). Numbers of B. brassicae on sprout plants with green and brown backgrounds varied greatly and did not differ significantly.In field cages, B. brassicae alatae were more attracted to potted sprout plants surrounded by bare soil than to ones surrounded by rings of living or cut grass or by artificial green rings. This effect was greater with small than with large sprout plants surrounded by grass rings.The maintenance of a limited weed cover is considered potentially useful in integrated control of some brassica pests.

Influence of crop background on natural enemies of aphids on Brussels sprouts

SUMMARYThe most abundant natural enemies of aphids on Brussels sprout crops were Syrphidae, different species being attracted differentially to weedy or weed‐free plots according to whether they were more host‐plant‐orientated (e.g. Melanostoma spp., Platycheirus spp.) and thus affected directly by the background, or more aphid‐orientated (e.g. Syrphus balteatus) and so less affected by background than by aphid numbers. Oviposition by Melanostoma spp. was usually much greater in weedy sprout crops than on sprouts in bare soil, and their eggs were also very abundant on weeds. Eggs of other syrphid species were scarcer on weeds. In contrast to Melanostoma, Platycheirus spp. usually oviposted preferentially on sprouts growing in bare soil. Oviposition by S. balteatus was in response to aphid abundance and thus tended to become greater on sprouts in bare soil. Notably more adults of non‐aphido‐phagous Syrphidae were caught over weedy than over non‐weedy Brussels sprout plants. Anthocoris nemorum nymphs and adults were very common on sprout plants and weeds in the weedy crop but were scarce on sprouts in bare soil; A. nemorum oviposited on white and yellow charlock (Raphanus raphanistrum and Sinapis arvensis) occasionally.Parasitism of Brevicoryne brassicae by Diaeretiella rapae appeared to be related to aphid numbers and was only indirectly influenced by the crop background.Field experiments with green and brown cloth backgrounds showed that some syrphids were attracted to green; A. nemorum was relatively scarce over both artificial backgrounds.It is concluded that decreased natural enemy action is partly responsible for the initially greater abundance of B. brassicae in a weed‐free crop of Brussels sprouts than in a weedy crop.

STIMULUS DURATION AS A MEASURE OF STIMULUS GENERALIZATION1

Four pigeons in the line-positive group were trained with a vertical line on a green background that signalled intermittent reinforcement while a plain green field signalled extinction. Four pigeons in the line-negative group were trained with the opposite discrimination. Response to a control key terminated any trial and initiated the next trial. The birds also used the control key during generalization tests to control the durations of trials in which various line orientations were presented. These durations were summed to provide generalization gradients of stimulus duration that were positive or negative in accordance with the trained discriminations. In Experiment 2, birds from the line-positive group were tested with a procedure in which the control key was not available on some trials. This provided an independent assessment of response rates to the test stimuli. These rates were used to predict the stimulus durations obtained when the control key was available. The findings supported a general model for the prediction of response distributions among concurrent stimuli from rates observed with single stimuli.

Incidental probability learning: Effects of task- relevant vs. irrelevant stimulus dimensions

Relative effects of probabilities associated with task-relevant and irrelevant stimuli were studied in a probability learning paradigm. Four groups of 24 subjects each received different training experiences prior to sequentially predicting 200 occurrences of a green or yellow color. For 200 training trials subjects predicted the shape of arrows outlined on a green or yellow background. During training the two arrow shapes and background colors varied on independent probability distributions (i.e., each dimension either 75:25 or 50:50); during testing the colors varied on a 75:25 schedule. Regardless of the distribution of background colors during training, subjects who received a 75:25 distribution of arrow shapes during training predicted significantly more occurrences of the more probable color during testing than did subjects who received a 50:50 distribution of arrow shapes. Thus, the frequency bias associated with task-relevant stimuli in a probability learning paradigm influenced subsequent predictions of another stimulus dimension, but the probability distribution of the irrelevant stimulus dimension in the first task did not affect subsequent prediction strategies for the same dimension.

Electrical responses of double cones in the turtle retina.

1. Responses to monochromatic flashes were recorded intracellularly from double cones in the retina of the turtle, Pseudemys scripta elegans. Double cones have been identified by intracellular marking with Procion Yellow dye.2. The direct light response of a double cone is a hyperpolarization graded with the intensity of a flash and similar to the response of single cones.3. When flashes were dim, responses were proportional to light intensity but varied in time course as a function of wave-length. They reached peak in about 120 msec for deep red stimuli and about 143 msec for green stimuli.4. When applied over red backgrounds, responses to red flashes became smaller, faster and frequently diphasic, but responses to green remained similar to those recorded from darkness. Green backgrounds made responses to all colours small and fast.5. Linear spectral sensitivity curves have peaks corresponding to the peak sensitivities of single red-sensitive and green-sensitive cones. Red and green backgrounds suppressed red and green sensitivity respectively.6. Large fields of illumination evoked composite responses which included the direct light response, its enhancement from illumination of nearby receptors and the depolarizing effect of luminosity horizontal cell impingement. In the green-sensitive element the depolarizing effect was larger for red than for green flashes, and stimulation with red annuli evoked net depolarizing responses.7. It is concluded that the responses of double cones may be explained by coupling of the responses from red-sensitive and green-sensitive elements each of which has properties otherwise similar to single red-sensitive and green-sensitive cones.

Interactions leading to horizontal cell responses in the turtle retina.

1. Small responses to large fields of dim monochromatic lights were recorded intracellularly from luminosity horizontal cells (L-cells), chromaticity horizontal cells (C-cells) and cones in the retinae of turtles, Pseudemys scripta elegans.2. Responses of cones to brief flashes applied over steady backgrounds were studied in order to interpret the corresponding responses of horizontal cells. Steady red or green backgrounds make the responses of red-sensitive cones smaller, faster and often diphasic. Green backgrounds have similar effects on the responses of green-sensitive cones to green flashes, but red backgrounds do not change them appreciably. Responses of double cones have properties intermediate between those of red and green cones.3. L-cells of both type I and type II are hyperpolarized by all visible wave-lengths, and their spectral sensitivity in the linear range resembles that of red cones. Their responses are not invariant with respect to colour, and their sensitivity to green relative to red stimuli increases during red backgrounds. These properties suggest that L-cells are activated mainly by red cones but also receive impingement from the red members of double cones.4. Spectral properties of red/green C-cells resemble those of green cones as modified by the recurrent action of L-cells. They can be explained assuming that red/green C-cells receive their principal impingement from green cones and subsidiary interactions from green/blue C-cells and the green members of double comes.5. The spectral sensitivity of the hyperpolarizing responses of green/blue C-cells is ascribed to impingement from blue cones. Their depolarizing responses have complex properties which suggest that they are brought about by the activity of both L-cells (probably through the blue cones) and red/green C-cells.6. It is concluded that the main properties of the responses of the horizontal cells can be explained by a simple circuit in which each horizontal cell is connected to a corresponding type of cone and the L-cells have a recurrent impingement on all cones. The scheme is modified by additional interactions which operate on the responses of each horizontal cell type.

A conjoint-measurement analysis of control by dimensions of compound stimuli.

3 chickens were trained on a go/no-go discrimination in which S+ was three white dots in a vertical array on a red background and S– was three white dots in a horizontal array on a green background. The nine combinations of red, yellow and green backgrounds with vertical, 45° and horizontal arrays of dots were presented in extinction. A conjoint-measurement analysis was discussed, and the orientation and color dimensions were shown to be independent and additive.

Retrieval of information from multiple ensembles in short-term memory

A recognition memory experiment investigated Ss' ability to organize information in short-term memory. A paradigm similar to that used by Sternberg was employed. A sequentially presented series of six digits (positive set) was shown with each digit appearing on a red, green, or amber background. The colors defined different ensembles, and responding to a test digit was contingent upon an item's membership in the positive set and the color-defined ensemble. Reaction time (RT) to the test digits indicated that Ss did organize information into ensembles. Furthermore, when informative cues were presented prior to the test item, Ss directed and confined their search to the cued subset.

Errorless Discrimination, Autoshaping, and Conditioned Inhibition

Pigeons were exposed to a discriminated autoshaping procedure in which brief presentation of a green light on a key was always followed by food whereas presentation of a vertical white line on the key was never followed by food. Pigeons acquired an errorless discrimination by pecking reliably in the presence of the green light but never in the presence of the line. The line inhibited pecking in later tests: when the white line was paired with food, key peck acquisition was retarded; and when the white line was superimposed on the green background, responding was suppressed.

Plant Effects on Host-Finding by Leiophron pseudopallipes (Hymenoptera: Braconidae), a Parasitoid of the Tarnished Plant Bug 1

The host-finding activity of Leiophron pseudopallipes Loan centers on flowering Erigeron plants. Several plant-related variables that could affect host-finding success were studied. These included plant height, plant density, host density per plant, the presence of unattractive plants in the habitat, and the background color of Lygus lineolaris (Palisot de Beauvois) feeding sites on the plants. Although the highest percentage of Lygus nymphs parasitized was associated with the same plant-height class in all fields sampled, plant height is probably unimportant in the host-finding behavior of L. pselldopallipes . Plant height is influenced by plant density, and evidence suggests that L. pselldopallipes is differentially attracted to areas of the habitat with the greatest density of Erigeron plants. Lygus densities are also higher where the Erigeron densities are greatest, which sometimes gives rise to a correlation between parasitization and Lyglis density. The presence of other herbs in Erigeron patches appears to lower the attractiveness of these stands to L. pseudopallipes . It is suggested that these plants may disrupt the olfactory cues used in host finding. The contrasting background color of the Erigeron plants also influenced parasitization. Reddish L. lineolaris nymphs, which tend to contrast with green plant background, were 3 times as apt to be parasitized as the green nymphs.