Foveal spatial summation in human cone mechanism

We measured at the fovea the chromatic contrast threshold for stimuli modulated along different chromatic directions in the isoluminant plane of MBDKL colour space, considering the two cardinal axes (L/M) and S/(L + M) and other intermediate non-cardinal directions. This psychophysical determination was conducted as a function of stimulus size. The test stimulus was a foveal isoluminant Gaussian patch with a raised cosinusoidal temporal profile superimposed on a neutral background. The task was performed binocularly. The increment threshold was measured for three observers by a Bayesian adaptive psychometric method (QUEST). The Ricco area of complete spatial summation was estimated from the threshold-versus-area curves. The perceptive fields are smaller for the L/M-cone opponent direction than the S/(L + M)-cone opponent. The perceptive field sizes for the stimuli in non-cardinal chromatic directions and stimuli modulated at the (L/M)-cone opponent direction present similar values. Measurements were made at two luminance levels, 5 and 40 cd m(-2), but the differences found were small. The perceptive field sizes found could be associated with LGN area.     

Movement-induced modulation of orientation-specific color aftereffects

The intensity of the McCollough effect is modified when, following exposure to the inducing chromatic stimuli, the achromatic test gratings are seen oscillating orthogonally to their orientations. Green aftereffect seen on stationary test gratings is enhanced by oscillations, while pink aftereffect present on the stationary gratings fades upon oscillation of the test stimulus. These opponent changes are tentatively accounted for in terms of an interaction between Fechner-Benham type induced color and processes that mediate the orientation-specific chromatic aftereffects.     

A ratio principle for a red/green and a yellow/blue channel?

There is strong empirical evidence that, under adaptation to another achromatic color stimulus, the lightness of an achromatic color stimulus depends on the ratio of the luminances of the two stimuli. In the present study, the suitability of this ratio principle is tested for two chromatic postreceptoral opponent channels. A Hering red/green channel and a non-Hering yellow/blue channel are specified as chromatic channels. The yellow/blue channel is defined by extrapolating the plane corresponding to unique green-white linearly to the reddish part of color space, using the plane’s surface as the channel’s equilibria. The experiment was run on an isoluminant plane, measured individually for each observer. Moving along an observer’s measured opponent axes, eight adaptation stimuli were selected for each channel and spanned the whole range of the channel’s coordinates. Red/green equilibria or yellow/blue equilibria were measured as excursions along the adaptation axes. For both presumed channels, the ratios of the equilibrium coordinates of test and adaptation stimuli were essentially constant. This supports the principle’s suitability. However, small asymmetries were found with respect to each channel’s opponent hues. The status of the proposed yellow/blue channel is discussed, as are conditions that might have favored the present findings.     

The L/M-opponent channel provides a distinct and time-dependent contribution towards visual recognition

The visual pathway has been successfully modelled as containing separate channels consisting of one achromatically opponent mechanism and two chromatically opponent mechanisms. However, little is known about how time affects the processing of chromatic information. Here, parametrically defined objects were generated. Reduced-colour objects were interleaved with full-colour objects and measures of recognition performance (d') were compared by the continuous serial recognition paradigm. Measures were taken at multiple delay intervals (1, 4, 7, and 10 s). When chromatic variations were removed, recognition performance was impaired, but at the 1 s and 10 s intervals only. When luminance variations were removed, no impairment resulted. When only L/M-opponent modulations were removed, a deficit in performance was produced only at the 1 s and 10 s intervals, similar to the removal of chromatic variation. When only S-opponent modulations were removed, no impairment was observed. The results suggest that the L/M-opponent pathway provides a specialised contribution to visual recognition, but that its effect is modulated by time. A three-stage process model is proposed to explain the data.     

The fluttering-heart illusion: a new hypothesis

The fluttering-heart illusion is a perceived lagging behind of a colour target on a background of a different colour when the two are oscillated together. It has been proposed that the illusion is caused by a differential in the perceptual latencies of different colours (Helmholtz 1867/1962), a differential in rod-cone latencies (von Kries 1896) and rod-cone interactions (von Grünau 1975, 1976 Vision Research 15 431-436, 437-440; 16 397-401; see list of references there). The purpose of this experiment was to assess the hypothesis that the fluttering-heart illusion is caused by a differential in the perceived velocities of chromatic and achromatic motion. To evaluate this hypothesis, we tested observers possessing normal colour vision and deuteranopes. The perceived delay of a chromatic target relative to an achromatic target was measured as a function of background cone contrast and target colour. For observers with normal colour vision, the perceived delay of the chromatic target is greater in the L-S than the L-M testing conditions. The reverse is observed in deuteranope observers. We suggest that this is caused by the absence of an L-M opponent mechanism contributing to chromatic motion in deuteranopes. Greater background cone contrasts tended to yield smaller perceived delays in both normal and deuteranope observers, indicating that greater chromatic modulation decreases the perceived delay of the colour target. These results support the hypothesis that the fluttering-heart illusion can be explained by a differential in the perceived velocities of chromatic and achromatic motion.     

The Stiles summation index applied to heterochromatic brightness matching

The summation index technique introduced by Stiles has been applied to heterochromatic brightness matching in order to explain individual differences in luminous efficiency functions for brightness. Such functions were obtained for 2-deg and 10-deg fields from twelve subjects, and the difference between the two fields was compared with the macular pigment density tabulated in Wyszecki and Stiles's book. A summation index was obtained for red and green stimuli combinations and the results are expressed in the form of an equation with nonlinear coefficients. The same equation is applied to the brightness luminous efficiency functions and the individual differences in the efficiency function are interpreted as the result of different contributions of opponent chromatic channels to the perception of brightness.     

Color adaptation in a yellow-blue system: proof of a simple numerical relationship]

Three axes in color space are specified: a (unique) yellow - (unique) blue axis, a (unique) green - magenta axis and brightness. Based on the two chromatic axes two linear opponent colors systems are defined: a red/green-system and a yellowish/bluish-system. A numerical relation is presented to describe color adaptation for the yellowish/bluish-system under adaptation to (unique) yellow and (unique) blue: two pairs of color stimuli are equivalent with regard to the yellowish/bluish-system - consisting of a test stimulus and an adaptation stimulus, respectively - if the ratios from the yellowish/bluish-coordinates of test stimulus and adaptation stimulus are identical. A control of brightness and the red/green-system is presupposed. For several (unique) yellow and (unique) blue adaptation stimuli it is examined how a test stimulus that appears neither yellowish nor bluish changes its location on the (unique) yellow - (unique) blue axis within color space. Three observers take part in the experiment. For each observer a plane of constant brightness and the opponent colors axes are estimated experimentally. The data show that the ratios from the yellowish/bluish coordinates of test stimulus and adaptation stimulus are essentially constant. The results are compared with analogous data for the red/green-system. The findings provide evidence for the specification of the three phenomenal axes. The specification is discussed with regard to Hering's opponent colors theory and Krauskopf's three "cardinal" axes [1982, Vision Research, 22, 1123-1131].     

Serotonin Augmentation Reduces Response to Attack in Aggressive Individuals

ABSTRACT— We tested the theory that central serotonin (5-hydroxytryptamine, or 5-HT) activity regulates aggression by modulating response to provocation. Eighty men and women (40 with and 40 without a history of aggression) were randomly assigned to receive either 40 mg of paroxetine (to acutely augment serotonergic activity) or a placebo, administered using double-blind procedures. Aggression was assessed during a competitive reaction time game with a fictitious opponent. Shocks were selected by the participant and opponent before each trial, with the loser on each trial receiving the shock set by the other player. Provocation was manipulated by having the opponent select increasingly intense shocks for the participant and eventually an ostensibly severe shock toward the end of the trials. Aggression was measured by the number of severe shocks set by the participant for the opponent. As predicted, aggressive responding after provocation was attenuated by augmentation of serotonin in individuals with a pronounced history of aggression.     

Electromyographic Analyses of Responses to Intergroup Threat

Two studies tested predictions from intergroup threat theory concerning emotional responses to intergroup threat. Study 1 employed threatening video clips of the 9/11/01 World Trade Center attacks. Study 2 employed video clips of a threatening “opponent” in a competition. Facial electromyography (EMG) was employed to capture emotion‐related muscle activity. As participants viewed videos in Study 1, they were instructed to consider Americans' reactions or their personal reactions. In Study 2, an “opponent” presented individually directed or group‐directed stereotype threat. Both studies provide support for the theory: Participants experiencing individual threats displayed greater EMG activity in muscles corresponding to inwardly directed emotions (fear), while participants experiencing group threats displayed greater EMG activity in muscles corresponding to outwardly directed emotions (anger).     

Aggression as a function of the intensity and pattern of attack

Forty Ss competed with an opponent in a reaction time task to avoid receiving shock. The opponent provided either consistently high intensity attack, increasing, decreasing, or consistently low attack. The S's shock settings for the opponent on each trial and ratings of the opponent after the task served as dependent measures. High intensity attack resulted in high intensity counterattack and negative ratings of the opponent. Low intensity attack resulted in low intensity counterattack and relatively positive ratings for the opponent. Decreasing attack resulted in decreasing counterattack and positive ratings of the opponent. Increasing attack resulted in increasing counterattack and comparatively high aggression ratings of the opponent.     

The reduction of attack instigated aggression

Thirty subjects competed with an opponent in a reaction time task to avoid receiving shock. The opponent initially set only the highest possible intensity shock for the subjects. The opponent then adopted one of three strategies to reduce the intensity of shocks set by the subjects. In one condition the opponent set shock intensities which matched those set by the subject. In a second condition the opponent set shocks which were not contingent upon those set by the subject but which were identical to those set by the opponent who matched the subject's settings. The opponent in the third condition suddenly reduced the intensity of his settings and chose only the least intense possible shock for the subject. All three conditions resulted in reduced aggression. This decrement was greatest and most rapid among those subjects who were exposed to a precipitous decrease in the intensity of attack.     

Interpersonal aggression as a function of subject's sex, subject's sex role identification, opponent's sex, and degree of provocation.

Ninety-five undergraduates served as subjects in an experiment where they could administer electric shock to an opponent and receive the same from an opponent. The independent variables were subject's sex, subject's sex role identification (as measured by the Bem Sex Role Inventory), opponent's sex, as well as degree of provocation from the opponent. Aggression was defined as level of shock chosen by the subject for the opponent. The results indicated that masculine subjects facing a male opponent were more aggressive than individuals of other sex role identifications whether or not they were provoked. It was also found that masculine males were more aggressive than other males or anyof the females. Furthermore, opponent's sex influenced the males' aggressiveness but had no effect on the degree of aggression in females. Finally, aggression increased in all subjects following increases in provocation. The results are discussed in terms of their implications for pyschological androgyny.     

Of matchers and maximizers: How competition shapes choice under risk and uncertainty

In a world of limited resources, scarcity and rivalry are central challenges for decision makers—animals foraging for food, corporations seeking maximal profits, and athletes training to win, all strive against others competing for the same goals. In this article, we establish the role of competitive pressures for the facilitation of optimal decision making in simple sequential binary choice tasks. In two experiments, competition was introduced with a computerized opponent whose choice behavior reinforced one of two strategies: If the opponent probabilistically imitated participant choices, probability matching was optimal; if the opponent was indifferent, probability maximizing was optimal. We observed accurate asymptotic strategy use in both conditions irrespective of the provision of outcome probabilities, suggesting that participants were sensitive to the differences in opponent behavior. An analysis of reinforcement learning models established that computational conceptualizations of opponent behavior are critical to account for the observed divergence in strategy adoption. Our results provide a novel appraisal of probability matching and show how this individually ‘irrational’ choice phenomenon can be socially adaptive under competition.     

The Y chromosome, social signals, and offense in mice

Offense is one type of aggression in mice (Mus musculus/Mus domesticus). Offense was measured in a panel of testers design for two congenic strains of mice. The two congenic strains were DBA1Bg and DBA1. C57BL10-YBg. These differ in the Y chromosome. Offense was measured for the following dyadic pairs: Group 1 (DBA1 tested against a DBA1 opponent); Group 2 (DBA1 tested against a DBA1.C57BL10-Y opponent); Group 3 (DBA1.C57BL10-Y tested against a DBA1.C57BL10-Y opponent); and Group 4 (DBA1.C57BL10-Y tested against a DBA1 opponent). Group 1 was more aggressive than Group 3, whereas Group 2 was no more aggressive than Group 4. Thus, when the experimental and opponent pairs have the same Y chromosome, the congenics differ in offense, whereas when the experimental and opponent pairs have different Y chromosomes, the congenics do not differ in offense. These findings are consistent with the hypothesis that these Y chromosomes affect the display of and response to social or other stimuli for offense of mice. These stimuli may be individual recognition chemosignals in urine.     

Reverse Discrimination and Aggressive Behavior

Aggression of each of 32 white male and female university students toward an opponent who had just defeated him in a competition was assessed in a 2 x 2 experimental design in which the winning opponent was either a black or a white and the loss was for one of two reasons: because the opponent 1) was economically deprived or 2) had superior ability. It was assumed that those S s who had lost to a black opponent because this person was economically deprived experienced reverse discrimination based on race. Results indicated that white S s were more aggressive toward a black when the loss was based on economic deprivation (reverse discrimination) than towards a white when the loss was due to economic deprivation (an arbitrary loss but not based on race), whereas white S s were less aggressive towards a black opponent than towards a white opponent when the S s lost because of the other's superior ability. The practical and theoretical implications of these results are discussed.     

An oblique effect of chromatic gratings measured by color-mixture thresholds

Contrast sensitivity is lower for obliquely oriented achromatic gratings than for vertical or horizontal gratings at high spatial and low temporal frequencies. Although this response is suggestive of mediation by P-pathway cortical correlates, no clear sensory (i.e. class 1) oblique effect has been demonstrated with isoluminant chromatic stimuli. In the present experiment, a two-alternative forced-choice detection task was used to measure observers' sensitivity to spatiotemporal sinusoids varying in orientation and color contrast. A maximum-likelihood method fit ellipses to the thresholds, with the length of each ellipse taken as a measure of chromatic contrast sensitivity at isoluminance, and the width as luminance contrast threshold. A chromatic oblique effect was observed at about 3 cycles deg-1 suggesting an orientation bias within the cortical stream conveying P-cell activity.     

TRANSITION FROM ROD TO CONE VISION: II. Successive contrast

S tabell , B. & S tabell , U. Transition from rod to cone vision. II. Successive contrast. Scad J. Psychol., 1969, 10 137–139—Transition from chromatic rod to chromatic cone activity during dark adaptation is interpreted as a kind of color mixing.     

Criticism in Need of Clarification

It furthers the dialectic when the opponent is clear about what motivates and underlies her critical stance, even if she does not adopt an opposite standpoint, but merely doubts the proponent’s opinion. Thus, there is some kind of burden of criticism. In some situations, there should an obligation for the opponent to offer explanatory counterconsiderations, if requested, whereas in others, there is no real dialectical obligation, but a mere responsibility for the opponent to cooperate by providing her motivations for being critical. In this paper, it will be shown how a set of dialogue rules may encourage an opponent, in this latter type of situation, to provide her counterconsiderations, and to do so at an appropriate level of specificity. Special attention will be paid to the desired level of specificity. For example, the critic may challenge a thesis by saying “Why? Says who?,” without conveying whether she could be convinced by an argument from expert opinion, or from position to know, or from popular opinion. What are fair dialogue rules for dealing with less than fully specific criticism?     

The opponent process theory and affective reactions

Solomon (1980) proposed an opponent process theory to account for motivational and affective dynamics. This theory asserts that the brain avoids extremes of emotional experience by countering the stimulation it receives with an opposite or opponent reaction. Opponent processes are thought to be responsible for the characteristic changes in affective experience that occur over time, and to account for the dynamics of affective response to such stimuli as skydiving and sauna bathing, which have heretofore been difficult to explain. However, the relevance of this theory for affective experiences in general (beyond physical stimuli and addictions) has yet to be demonstrated. The present paper examines opponent process theory predictions in two settings, involving affective responses to situation-scenarios and emotion-provoking slides. In each study, significant habituation to both positive and negative affective stimuli was found, as the opponent process theory would predict. Subjects also showed a reversal of affect when the stimuli were reversed from positive to negative or vice versa. However, contrary to opponent process theory predictions, there was no evidence that withdrawal responses were greater after habituation to the affective stimulus. The only instance of a significant difference in withdrawal responses was actually in a direction opposite to that which the opponent process theory predicts. All other predicted differences were not significant. The opponent process theory, therefore, was not supported in these data and appears to need revision or qualification as to its domains of application.