Extremely long-term persistence of the McCollough effect.

The question has been raised whether an associative mechanism is responsible for the persistence of the McCollough effect. Since current estimates of its rate of decay are derived from procedures in which subjects are repeatedly tested, it was hypothesized that the measured effects might be attenuated by the testing process. Accordingly, a comparison was made between repeated testing and time-elapse testing. A conventional group of 16 subjects had repeated testing at 0, 8, 24, 56, and 120 hr. after induction. Five other groups of 16 were run, each at one of the time delays, with no intervening tests; an additional measure was taken where appropriate at 120 hr. A magenta-green nulling procedure was used to assess the aftereffect. The repeated-test group showed a linear decrease of effect against the stated delays, reaching zero at 120 hr. In contrast, the time-elapse groups showed little decline up to 120 hr. Those groups retested at 120 hr. showed declines due to prior testing. When four more groups were subsequently tested at intervals up to 2,040 hr., the effect remained at better than half strength.     

Negative afterimages and the McCollough effect

Four experiments were conducted to test earlier claims about the relationship between the negative afterimage and the McCollough effect. The first claim (Hansel & Mahmud, 1978) is that long-lasting afterimages occur when induced by the same alternating-stimulus procedure as that used to induce the McCollough effect. The second claim (Murch & Hirsch, 1972) is that afterimages can themselves induce McCollough effects if they are induced and paired sequentially with grating patterns. In testing these claims, a reliable computer-controlled color-cancellation technique developed earlier was used to measure the apparent color of both afterimages and McCollough effects objectively. No support was found for the first claim following alternative presentation of two homogeneously colored regions for total periods of 5 min (Experiment 1) and 20 min (Experiment 2). The second claim was fully supported: After an induction period of 7.3 min, a McCollough effect occurred for a red-vertical pairing but not for a green-horizontal pairing (Experiment 3); but after an induction period of 20 min, McCollough effects occurred strongly for both pairings (Experiment 4). The theoretical implications of these outcomes are considered in the context of recent theories of color and pattern processing in the visual system.     

Spatial-frequency-contingent color aftereffects: Adaptation with one-dimensional stimuli

The McCollough effect was shown to be spatial-frequency selective by Lovegrove and Over (1972) after adaptation with vertical colored square-wave gratings separated by 1 octave. Adaptation with slide-presented red and green vertical square-wave gratings separated by 1 octave failed to produce contingent color aftereffects (CAEs).However, when each of these gratings was adapted alone, strong CAEs were produced. Adaptation with vertical colored sine-wave gratings separated by 1 octave also failed to produce CAEs, but strong effects were produced by adaptation with each grating alone. By varying the spatial frequency of the test sine wave, CAEs were found to be tuned for spatial frequency at 2.85 octaves after adaptation of 4 cycles per degree (cpd) and at 2.30 octaves after adaptation of 8 cpd. Adaptation of both vertical and horizontal sine-wave gratings produced strong CAEs, with bandwidths ranging from 1.96 to 2.90 octaves and with lower adapting contrast producing weaker CAEs. These results indicate that the McCollough effect is more broadly tuned for spatial frequency than are simple adaptation effects.     

Instrumental performance following reinforcer devaluation depends upon incentive learning

Conditioning an aversion to the reinforcer following instrumental training reduces performance in a subsequent extinction test. Three experiments examined whether this reinforcer-devaluation effect depends upon experience with the devalued reinforcer prior to the extinction test. In Experiments 1 and 2 thirsty rats were trained to press a lever for sucrose solution in a single session. All animals then received an injection of lithium chloride (LiCl) either immediately following the session or after a delay of 6 hr. On the next day either the sucrose solution or water was presented non-contingently either in the operant chamber without the lever present or in a separate drinking cage. In a subsequent extinction test only the animals that had received immediate LiCl and re-exposure to non-contingent sucrose pressed less than those in the delayed-LiCl control groups. Experiment 3 demonstrated that this difference depended, at least in part, on post-conditioning exposure to a contingent reinforcer. Lever pressing and chain pulling were reinforced concurrently with either a sucrose or a sodium chloride solution in a single session immediately before the administration of LiCl. All animals then received non-contingent presentations of one of the reinforcers in the absence of both manipulanda. Finally, performance of both actions was assessed in an extinction test. Re-exposure to a reinforcer produced a relative reduction in the performance of its associated action on test. These results are interpreted as evidence that the instrumental reinforcer devaluation effect depends upon a process of incentive learning.     

利用反诱导消除McCollough效应

ＭｃＣｏｌｌｏｕｇｈ效应在完全黑暗和自然视觉条件下的消退过程很缓慢,而利用同频补色条栅来进行反诱导,能在十几分钟内消除显色效应。消除所用时间与反诱导条栅的亮度、颜色和栅条间距（空间频率）有关。进一步说明导致ＭｃＣｏｌｌｏｕｇｈ效应恢复平衡的主要因素跟网膜刺激方式有关。     

Spatial-frequency-contingent color aftereffects: adaptation with one-dimensional stimuli.

The McCollough effect was shown to be spatial-frequency selective by Lovegrove and Over (1972) after adaptation with vertical colored square-wave gratings separated by 1 octave. Adaptation with slide-presented red and green vertical square-wave gratings separated by 1 octave failed to produce contingent color aftereffects (CAEs). However, when each of these gratings was adapted alone, strong CAEs were produced. Adaptation with vertical colored sine-wave gratings separated by 1 octave also failed to produce CAEs, but strong effects were produced by adaptation with each grating alone. By varying the spatial frequency of the test sine wave, CAEs were found to be tuned for spatial frequency at 2.85 octaves after adaptation of 4 cycles per degree (cpd) and at 2.30 octaves after adaptation of 8 cpd. Adaptation of both vertical and horizontal sine-wave gratings produced strong CAEs, with bandwidths ranging from 1.96 to 2.90 octaves and with lower adapting contrast producing weaker CAEs. These results indicate that the McCollough effect is more broadly tuned for spatial frequency than are simple adaptation effects.     

Orientation-contingent color aftereffects mediated by subjective transparent structures.

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n = 6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeared more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes. Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Rolipram reverses scopolamine-induced and time-dependent memory deficits in object recognition by different mechanisms of action

In this study, the effect of the selective phosphodiesterase type 4 (PDE4) inhibitor rolipram on memory performance was investigated using the object recognition task. First, three doses of rolipram (0.01, 0.03 or 0.1 mg/kg) were tested with a 24h delay between the learning (T1) and the test (T2) trial. Doses of rolipram were injected at different time points (30 min before T1, immediately after T1 or 3 h after T1). In a second experiment, the effects of rolipram (0.03, 0.1 or 0.3 mg/kg) were tested in combination with scopolamine (0.1 mg/kg) applying a 1 h delay between trials. Both substances were administered 30 min before T1. Using a 24h interval, rolipram showed an improvement in long-term memory performance when injected 3 h after T1 at a dose of 0.03 mg/kg. Further, rolipram reversed the scopolamine-induced short-term memory deficit at a dose of 0.1 mg/kg. Although the improved memory performance in both conditions is likely to be explained by elevated cAMP levels, two separate working mechanisms might explain these effects.     

Differential roles of hippocampal metabotropic glutamate receptors 1 and 5 in inhibitory avoidance learning

Group I metabotropic glutamate receptors (mGlu1 and 5) have been implicated in synaptic plasticity and learning and memory. However, much of our understanding of how these receptors in different brain regions contribute to distinct memory stages in different learning tasks remains incomplete. The present study investigated the effects of the mGlu5 receptor antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), and mGlu1 receptor antagonist, (S)-(+)-alpha-amino-4-carboxy-2-methylbenzene-acetic acid (LY 367385) in the dorsal hippocampus on the consolidation and extinction of memory for inhibitory avoidance learning. Male, Sprague-Dawley rats were trained in a single-trial step-down inhibitory avoidance task. MPEP, LY 367385 or saline were infused bilaterally into the CA1 region immediately after training or immediately after the first retention test which was given 24h after training. Rats receiving MPEP (1.5 or 5.0 microg/side) or LY 367385 (0.7 or 2.0 microg/side) infusion exhibited a dose-dependent decrease in retention when tested 24h later. MPEP was ineffective while LY 367385 significantly attenuated extinction when injected after the first retention test using an extinction procedure. These findings indicate a selective participation of hippocampal group I mGlu receptors in memory processing in this task.     

Color-luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color-luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color-luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color-luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

Orientation-contingent color aftereffects mediated by subjective transparent structures

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n=6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeased more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes, Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

The effect of discrimination training on responses to a new stimulus

Most previous research on the effect of the duration of preceding discrimination training on responding to a new stimulus has measured the responding during extinction. To reduce effects originating in the extinction procedure itself, the present study assessed the effect of discrimination training on responses to a new negative stimulus added during continued discrimination training. Pigeons were given a new negative stimulus (blue key) after 0, 1, 3, or 9 days of discrimination training with a yellow key as the positive stimulus, and both a green key and a red key as negative. Fewer responses were made to the blue key when it was introduced after nine days of discrimination training than after less discrimination training. That effect of long discrimination training agrees with reported results from extinction tests. However, the effect of briefer discrimination training in the present study differed from reported results with extinction testing. It appears that testing during continued discrimination training eliminates a distortion present in extinction tests of the effect of discrimination training on responding to a new stimulus.     

Color—luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color—luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color—luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color—luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

An assessment of the role of handling cues in "spontaneous recovery" after extinction

Three experiments examined the assertion that presession handling cues that accompany training with reinforcement might account for spontaneous recovery when they reoccur following extinction. In Experiment 1, after extensive training on a variable-interval schedule, key pecking in pigeons was extinguished following either normal or distinctively different handling and transportational cues. Those cues resulted in enhanced spontaneous recovery 24 hr later when normal cues were reinstated. In Experiment 2, however, subjects tested following the normal handling cues showed no more spontaneous recovery than did subjects that spent the entire extinction-test interval in the experimental chambers and thus were tested without handling cues altogether. In Experiment 3, a group whose test for recovery began 10 min after being placed in the chambers yielded as much spontaneous recovery as did a group tested normally. Furthermore, a group for which extinction began at mid-session and for which handling therefore could not be a discriminative cue for extinction showed no more spontaneous recovery than did the other two groups. Handling cues thus contributed to spontaneous recovery only after explicit discrimination training, as provided in Experiment 1.     

Retention of Conditioned Inhibition Produced by Extinction

Rats in a flavor aversion procedure were used to examine the extent to which an extinguished CS can pass a retardation and summation test for conditioned inhibition after either a short or a long retention interval. Rats were given a single pairing of a flavored solution with LiCl, and then received a large number of CS-alone extinction trials. Following extinction, some subjects received a 3-week retention interval following extinction while others did not. Extinction produced evidence of conditioned inhibition on both tests when a short retention interval occurred following extinction. However, conditioned inhibition was attenuated by the long retention interval when assessed with a retardation test, but no effect of the long retention interval was observed when inhibition was evaluated with a summation test.     

Lesions of rat infralimbic cortex enhance recovery and reinstatement of an appetitive Pavlovian response

The prefrontal cortex (PFC) has a well-established role in the inhibition of inappropriate responding, and evidence suggests that the infralimbic (IL) region of the rat medial PFC (MPFC) may be involved in some aspects of extinction of conditioned fear. MPFC lesions including, but not those sparing the IL cortex increase spontaneous recovery of extinguished conditioned fear when tested 24 h after an initial extinction session. The current experiment extended these findings by use of appetitive rather than aversive conditioning. Ten IL-lesioned and 11 sham-operated rats were trained on a Pavlovian task in which a conditioned stimulus (CS) was followed by food pellets (the unconditioned stimulus or US). IL lesions had no effect on extinction of the conditioned response (CR, magazine entries) during the first extinction session. However, the level of spontaneous recovery between the first extinction session and a second, 24 h later, was increased in IL-lesioned rats relative to sham animals. In contrast, evidence of savings measured between the extinction sessions did not differ between groups. Furthermore, reinstatement of the CR following unsignaled delivery of the US was also increased in IL-lesioned rats.     

Chronic stress and sex differences on the recall of fear conditioning and extinction

Chronic stress effects and sex differences were examined on conditioned fear extinction. Male and female Sprague–Dawley rats were chronically stressed by restraint (6 h/d/21 d), conditioned to tone and footshock, followed by extinction after 1 h and 24 h delays. Chronic stress impaired the recall of fear extinction in males, as evidenced by high freezing to tone after the 24 h delay despite exposure to the previous 1 h delay extinction trials, and this effect was not due to ceiling effects from overtraining during conditioning. In contrast, chronic stress attenuated the recall of fear conditioning acquisition in females, regardless of exposure to the 1 h extinction exposure. Since freezing to tone was reinstated following unsignalled footshocks, the deficit in the stressed rats reflected impaired recall rather than impaired consolidation. Sex differences in fear conditioning and extinction were observed in nonstressed controls as well, with control females resisting extinction to tone. Analysis of contextual freezing showed that all groups (control, stress, male, female) increased freezing immediately after the first tone extinction trial, demonstrating contextual discrimination. These findings show that chronic stress and sex interact to influence fear conditioning, with chronic stress impairing the recall of delayed fear extinction in males to implicate the medial prefrontal cortex, disrupting the recall of the fear conditioning acquisition in females to implicate the amygdala, and nonstressed controls exhibiting sex differences in fear conditioning and extinction, which may involve the amygdala and/or corticosterone levels.     

Contour specificity of the McCollough effect

Subjective estimates of McCollough aftereffect strength are significantly reduced when certain spatial features of the line grating patterns are manipulated. Results are dependent upon whether the spatial parameters of the test or inspection patterns are altered. Changing the angular slant, contour sharpness, or contour completeness of the inspection gratings does not affect aftereffect strength, but changing the spatial frequency, contour sharpness, or contour completeness of the test gratings does. The implications of these results are discussed with regard to theories offered to explain the McCollough effect.     

ACTH produces long-lasting recovery following partial extinction of an active avoidance response

Recent data suggest that ACTH administration produces recovery of an extinguished passive avoidance response at an unusually long injection-to-test interval. The present experiment sought to explore further the durability of recovery by examining the effect of ACTH following extinction of one-way active avoidance. Adult rats were injected with 16 IU ACTH, an equivalent volume of the ACTH vehicle gel, or saline 48 h after a previously learned active avoidance response was partially extinguished. Different groups from each treatment condition were tested 15 min, 24 h, or 7 days after injection. ACTH improved avoidance performance at all injection-to-test intervals relative to saline and vehicle gel injected controls. These data indicate that unlike reversal of other types of performance decrements, in which the effect of ACTH appears to be transient, administration of the hormone following an extinction treatment can produce enduring improvement of avoidance performance.     

Positive contrast, negative induction, and inhibitory stimulus control in the rat

In Experiment I, 24 rats were trained on a multiple variable-interval variable-interval schedule with a doorlight and white noise serving as component cues. Two groups were then shifted to a multiple extinction variable-interval schedule, and a third group was maintained on the multiple variable-interval variable-interval schedule. The multiple extinction variable-interval condition produced positive contrast when either the light or noise signalled extinction, and both of these cues acquired inhibitory stimulus control as measured by a combined cue test. In Experiment II, the multiple variable-interval variable-interval condition was shifted to multiple extinction variable-interval for one group, to multiple variable-time variable-interval for a second group, and was unchanged for the third group. The two experimental conditions produced identical patterns of response-rate reduction in the altered component, but the multiple extinction variable-interval condition produced positive contrast, whereas the multiple variable-time variable-interval condition did not. Subsequent combined cue and resistance to reinforcement tests revealed that the cue signalling extinction acquired stronger inhibitory stimulus control than the cue signalling variable time.