Correlation-based development of ocularly matched orientation and ocular dominance maps: determination of required input activities

We extend previous models for separate development of ocular dominance and orientation selectivity in cortical layer 4 by exploring conditions permitting combined organization of both properties. These conditions are expressed in terms of functions describing the degree of correlation in the firing of two inputs from the lateral geniculate nucleus (LGN), as a function of their retinotopic separation and their "type" (ON center or OFF center and left eye or right eye). The development of ocular dominance requires that the correlations of an input with other inputs of the same eye be stronger than or equal to its correlations with inputs of the opposite eye and strictly stronger at small retinotopic separations. This must be true after summing correlations with inputs of both center types. The development of orientation-selective simple cells requires that (1) an input's correlations with other inputs of the same center type be stronger than its correlations with inputs of the opposite center type at small retinotopic separation; and (2) this relationship reverse at larger retinotopic separations within an arbor radius (the radius over which LGN cells can project to a common cortical point). This must be true after summing correlations with inputs serving both eyes. For orientations to become matched in the two eyes, correlated activity within the receptive fields must be maximized by specific between-eye alignments of ON and OFF subregions. Thus the correlations between the eyes must differ depending on center type, and this difference must vary with retinotopic separation within an arbor radius. These principles are satisfied by a wide class of correlation functions. Combined development of ocularly matched orientation maps and ocular dominance maps can be achieved either simultaneously or sequentially. In the latter case, the model can produce a correlation between the locations of orientation map singularities and local ocular dominance peaks similar to that observed physiologically. The model's main prediction is that the above correlations should exist among inputs to cortical layer 4 simple cells before vision. In addition, mature simple cells are predicted to have certain relationships between the locations of the ON and OFF subregions of the left and right eyes' receptive fields.     

Development of ocular dominance.

Tested sighting dominance in the eyes of 68 infants (mean age = 44.5 wks), 62 elementary school children (mean age = 9.0 yrs), and 86 adults (mean age = 25.2 yrs), using a green point of light brought toward the median plane. 3 trials were administered to each S. In each group more Ss were right-eye than left-eye dominant, values not differing significantly from the adult norm of 65% right-eye dominant. Eye preference was consistent in all 3 trials for adults and children, but only about half the infants consistently chose the same eye in all trials. The implications of the data are methodological, indicating that optical dominance can be measured in preverbal Ss, and developmental, indicating no significant changes in sighting dominance with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of ocular dominance on the performance of professional baseball players

OBJECTIVE: The purpose of the study was to determine whether a performance difference exists between baseball players with "same" (right-right) and "crossed" (right-left) hand-ocular dominance. DESIGN: A cohort study design was used. PARTICIPANTS: Four hundred and ten major and minor league members of the Los Angeles Dodgers professional baseball team. INTERVENTION: Measurement of ocular dominance. MAIN OUTCOME MEASURES: Batting average and earned run average (ERA). RESULTS: Same/crossed dominance (with P values in parentheses) are as follows: Batting averages: major league-0.271/0.251 (0.20); minor league-0.274/0.270 (0.57); ERA: major league-3.34/3.56 (0.66); minor league-4.00/4.20 (0.54). CONCLUSIONS: Hand-ocular dominance patterns do not have an effect on batting average or ERA.     

Right-wing authoritarianism, social dominance orientation, and prejudice.

Right-wing authoritarianism and social dominance orientation have been proposed as 2 major individual difference variables underlying prejudice. This study examined the relationships of these variables to 3 forms of prejudice—affective responses, stereotyping, and attitudes toward equality enhancement—directed at 2 social groups—African Americans and homosexuals. Canonical correlation analyses showed that social dominance orientation was related to most forms of prejudice directed toward both groups and that right-wing authoritarianism was related to affective responses to and stereotyping of homosexuals. In addition, it was found that, as predicted by the social dominance model, stereotyping mediated the relationships between social dominance orientation and other forms of prejudice and that social dominance orientation mediated gender differences in expressions of prejudice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of neural activity and intracortical connectivity on the periodicity of ocular dominance stripes

A mechanism for the precise excision of DNA between two target sites was elucidated by analysing the individual steps during the reactions of the SfiI endonuclease on a plasmid with two SfiI sites. Previous studies had indicated that SfiI is a tetrameric protein that binds to two copies of its recognition site before cleaving both sites in both strands. In this study, the concerted cleavage of four phosphodiester bonds was shown to arise from four consecutive reactions that had similar values for their intrinsic rate constants. Each reaction is presumably mediated by one of the four active sites in the tetramer and all four were generally completed within the life-time of the complex between the protein and two recognition sites, though products cleaved in one or two phosphodiester bonds were also detected following premature dissociation of the enzyme-substrate complex at elevated temperatures. At the physiological temperature for this enzyme, all four bonds were cleaved within one minute but the subsequent dissociation of the enzyme-product complex, liberating the excised segment of DNA, took about one hour. The tetrameric structure for SfiI was confirmed by equilibrium centrifugation.     

The orientation and direction selectivity of cells in macaque visual cortex

Quantitative data are presented on the orientation and direction specificity of the responses of cells in macaque monkey striate cortex. There is a bimodal distribution of direction-specific and nondirection-specific cells, with similar orientation tuning in each class. Cells range in orientation bandwidth at half amplitude from 6 degrees to 360 degrees (i.e. no orientation tuning), with a median near 40 degrees. Foveal-parafoveal and simple-complex subsamples show similar ranges of orientation bandwidths as well as similar medians (the bandwidths being somewhat broader than those found in cat cortex). The foveal subsample and a high-spatial-frequency subsample have more horizontal and vertical optimal orientations than oblique ones. Most cells show inhibition to some orientations, as well as excitation to others. Minimum-response orientations are generally less than 90 degrees from the optimal orientation--indicating maximum inhibition adjacent to the excitatory orientations. Three simple receptive field models are shown to differ in their abilities to account for these results.     

Development of oriented ocular dominance bands as a consequence of areal geometry

BACKGROUND: Breast cancer has become a national health problem, affecting more than 180,000 women each year. Although advances in early detection and treatment have been made, it remains the second leading cause of cancer-related death in women. KEY POINTS: The treatment of breast cancer requires the careful integration of systemic and local methods. Although the application of hormonal therapy or chemotherapy is becoming less distinct, this discussion will review the important clinical trials and future directions of chemotherapy in the management of breast cancer. Data support the use of chemotherapy in the adjuvant setting, for preoperative tumor reduction of locally advanced disease, and as palliation in metastatic disease. The optimal chemotherapeutic regimen is not known; however, data support a role for adjuvant doxorubicin in node-positive disease, neoadjuvant therapy for high-risk disease, and high-dose chemotherapy to consolidate responding metastatic disease. CONCLUSIONS: The clinician must determine the risks and potential benefits of systemic chemotherapy before recommending treatment strategies. Although progress has been made, future advances can only occur through active participation in clinical trials.     

Injection of MK-801 affects ocular dominance shifts more than visual activity

Kittens were given intramuscular injections of the N-methyl--aspartate (NMDA) antagonist MK-801 twice daily (morning and midday) during the peak of the period of susceptibility for ocular dominance changes. They were then exposed to light with one eye closed for 4 h after each injection. The ocular dominance of these kittens was shifted significantly less than that of kittens injected with saline and exposed to light over the same period at the same age. After recording a sample of cells for an ocular dominance histogram, the kittens were injected with the same dose of MK-801 that was used during rearing to observe its effect on the activity of single cells in the visual cortex. In the majority of cells (7/13) there was no significant change in activity. Positive evidence for a reduction in activity was seen in only a minority (3/13) of cells. In a separate series of experiments, dose-response curves were measured for cells in the visual cortex in response to iontophoresis of NMDA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and the effect of an injection of MK-801 on these curves was measured. MK-801, at doses similar to those used in the ocular dominance experiments, had a significant effect on the dose-response curves for NMDA, but little effect on the dose-response curves for AMPA, or the visual responses of the cells. We conclude that ocular dominance shifts can be reduced significantly by a treatment that has little effect on the level of activity of cells in the visual cortex but does specifically affect the responses of the cells to NMDA as opposed to the responses to AMPA.     

Pattern of ocular dominance columns in human striate cortex in strabismic amblyopia

Previous experiments in animals have shown that early unilateral eyelid suture, a model of amblyopia induced by cataract, causes shrinkage of ocular dominance columns serving the deprived eye in the striate cortex. It is unknown whether the ocular dominance columns are affected in amblyopia produced by strabismus. We examined specimens of striate cortex obtained postmortem from a 79-year-old woman with a history of amblyopia in her left eye (20/800) since age 2 from accommodative esotropia. Four years prior to her death, she suffered an ischemic infarct of the left optic disc. This injury to the left optic disc made it possible to label the ocular dominance columns using cytochrome oxidase histochemistry. The pattern of ocular dominance columns was reconstructed throughout most of the right striate cortex. No shrinkage of columns was found. In the left cortex only half the column mosaic was labelled, because the patient had some residual vision in the temporal retina of her left eye. The columns within the labelled portion of the overall mosaic appeared normal. These findings indicate that shrinkage of ocular dominance columns does not occur in humans with amblyopia caused by accommodative esotropia. The ocular dominance columns are probably no longer susceptible to shrinkage at the age when most children with this condition begin to develop amblyopia.     

A model of ocular dominance column development by competition for trophic factor

Recent experimental evidence has shown that application of certain neurotrophic factors (NTs) to the developing primary visual cortex prevents the development of ocular dominance (OD) columns. One interpretation of this result is that afferents from the lateral geniculate nucleus compete for postsynaptic trophic factor in an activity-dependent manner. Application of excess trophic factor eliminates this competition, thereby preventing OD column formation. We present a model of OD column development, incorporating Hebbian synaptic modification and activity-driven competition for NT, which accounts for both normal OD column development as well as the prevention of that development when competition is removed. In the "control" situation, when available NT is below a critical amount, OD columns form normally. These columns form without weight normalization procedures and in the presence of positive inter-eye correlations. In the "experimental" case, OD column development is prevented in a local neighborhood in which excess NT has been added. Our model proposes a biologically plausible mechanism for competition between neural populations that is motivated by several pieces of experimental data, thereby accounting for both normal and experimentally perturbed conditions.     

Social dominance orientation: A personality variable predicting social and political attitudes.

Social dominance orientation (SDO), one's degree of preference for inequality among social groups, is introduced. On the basis of social dominance theory, it is shown that (1) men are more social dominance-oriented than women, (2) high-SDO people seek hierarchy-enhancing professional roles and low-SDO people seek hierarchy-attenuating roles, (3) SDO was related to beliefs in a large number of social and political ideologies that support group-based hierarchy (e.g., meritocracy and racism) and to support for policies that have implications for intergroup relations (e.g., war, civil rights, and social programs), including new policies. SDO was distinguished from interpersonal dominance, conservatism, and authoritarianism. SDO was negatively correlated with empathy, tolerance, communality, and altruism. The ramifications of SDO in social context are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social dominance orientation and the political psychology of gender: A case of invariance?

Social dominance theory assumes transsituational and transcultural differences between men and women in social dominance orientation (SDO), with men showing higher levels of SDO than women. SDO is a general individual-difference variable expressing preference for superordinate in-group status, hierarchical relationships between social groups, and a view of group relations as inherently 0-sum. Data from a random sample of 1,897 respondents from Los Angeles County confirmed the notion that men have significantly higher social dominance scores than women and that these differences were consistent across cultural, demographic, and situational factors such as age, social class, religion, educational level, political ideology, ethnicity, racism, region of national origin, and gender-role relevant opinion. The theoretical implications are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A biophysical model for the developmental time course of retinal orientation selectivity

A quantitative study of the time course of development of the percentage of orientationally selective and isotropic ganglion cells in turtle retina has recently been performed. This study revealed that as soon as ganglion cells start responding to light, a large percentage of them are selective to the orientations of moving visual stimuli. This percentage decreases with age to reach a minimum around hatching, increases dramatically after birth and finally, decreases again following the first month of life to reach adult level. Concomitantly, the percentage of cells responding isotropically to the orientation of elongated stimuli increases monotonically until about 30 days after birth, stabilizing afterwards. To account for both time courses, we propose a biophysical model implementing features ubiquitous to developing vertebrate retinas. These features include early dendritic and synaptic spatial polarization, dendritic growth, and waves of activity generated spontaneously or by visual stimulation sweeping across the inner plexiform layer (IPL). The model also assumes a physiologically plausible Hebbian rule, which includes long-term potentiation and depression. Computer simulations of this model yield good fits of the data. The quality of these fits confirms and extends results from an earlier model using computationally-simple mechanisms, which suggested that early dendritic polarization might be the seed for mature orientation selectivity.     

Determining ligand orientation and transphosphonylation mechanisms on acetylcholinesterase by Rp, Sp enantiomer selectivity and site-specific mutagenesis

Acetylcholinesterase, an enzyme of the serine hydrolase family, catalyzes the rapid hydrolysis of certain carboxyl esters. Other acyl esters efficiently transacylate the enzyme with a subsequent, slow deacylation step. Of these, the phosphoryl and phosphonyl esters are perhaps of greatest mechanistic interest since individual enantiomers of known absolute stereochemistry can be isolated and their interactions with the dissymmetric enzyme active site examined. We describe here studies of a series of enantiomeric Rp- and Sp-alkylphosphonates interacting with mouse acetylcholinesterase. Since the acetylcholinesterase is generated by recombinant DNA methods, mutant enzymes can be made with specific replacements of individual amino acid side chains. Individual amino acid replacements in the acyl pocket, the choline subsite and at the active center gorge entry have been generated, and the reaction kinetics of the mutant enzymes analyzed. These studies have shown that substitution of aliphatic amino acids for phenylalanines 295 and 297 in the acyl pocket diminishes, and in some cases, actually inverts chiral preferences. The combined structure-activity approach, where both ligand and enzyme are modified systematically, has enabled us to show that the restricted dimensions of the acyl pocket in the active center dictate enantiomeric selectivity. Moreover, the reactions of compounds of known absolute stereochemistry show three requirements for efficient transphosphonylation: (a) apposition of the phosphate with the gamma-oxygen on Ser 203 to form a pentavalent, presumed trigonal bipyramidal intermediate, (b) polarization of the phosphonyl oxygen bond by its positioning in the oxyanion hole, and (c) positioning the leaving group towards the gorge exit.     

Transneuronal WGA-HRP: can it demonstrate development of ocular dominance patches and effects of monocular deprivation?

We have attempted to use intraocular injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to label ocular dominance patches in developing layer 4 of cat visual cortex. The cortices of animals killed at 49 days or later showed normal ocular dominance patches similar to those seen in [3H]proline material. Animals killed at 42 days showed some patches, but also showed unsegregated regions. Animals killed younger were difficult to stain and did not have patches. We also examined the ability of the WGA-HRP technique to demonstrate the effects of monocular deprivation (MD). MD for the first 3 months of life produced expansion of the afferents from the nondeprived eye and retraction of the patches from the deprived eye. One week of MD at about 5 weeks of age produced an expansion of the patches innervated by the nondeprived eye, but did not obviously affect the patches innervated by the deprived eye. We conclude that WGA-HRP is useful for examining the effects of long-term MD on ocular dominance patches but not for following the development of segregation. Its advantages over the [3H]proline technique are that it does not require a delay of many weeks before the sections can be examined and is much less expensive.     

Managing discrimination in selection: The influence of directives from an authority and social dominance orientation.

The authors examined one manner in which to decrease the negative impact of social dominance orientation (SDO), an individual difference variable that indicates support for the domination of 'inferior' groups by 'superior' groups (J. Sidanius & F. Pratto, 1999, p. 48), on the selection of candidates from low-status groups within society. Consistent with the tenets of social dominance theory, in 2 studies we found that those high in SDO reported that they were less likely to select a potential team member who is a member of a low-status group (i.e., a White female in Study 1 and a Black male in Study 2) than those low in SDO. However, explicit directives from an authority moderated this effect such that those high in SDO were more likely to select both candidates when authority figures clearly communicated that job performance indicators should be used when choosing team members. Thus, our studies suggest that the negative effects of SDO may be attenuated if those high in SDO are instructed by superiors to use legitimate performance criteria to evaluate job candidates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of estrogen level on food-seeking dominance among male rats.

Daily paired 6 male hooded rats against each other in all combinations on a competitive food-seeking task. Trials against 1 confederate submissive and 1 dominant S were interspersed with the daily pairings for each hierarchical S in order to equate their total wins and losses. Following stabilization, the top 3 Ss were injected with estradiol benzoate prior to each day's pairings. This resulted in a temporary disruption of the hierarchy as the treated Ss gradually worked their way to the bottom of the hierarchy which then restabilized in that order. Subsequent withdrawal of treatment led to the gradual reestablishment of the original pretreatment hierarchy. Estrogen is thus seen to have an effect opposite in direction to that of testosterone on dominance among male rats. Unlike testosterone, however, the effect did not long outlast the treatment. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Authoritarian dynamics and unethical decision making: High social dominance orientation leaders and high right-wing authoritarianism followers.

When dilemmas require trade-offs between profits and ethics, do leaders high in social dominance orientation (SDO) and followers high in right-wing authoritarianism (RWA) make decisions that are more unethical than those made by others? This issue was explored in 4 studies with female participants performing managerial role-playing tasks. First, dyads comprising a person who was either low or high in SDO and a person who was either low or high in RWA negotiated for a leadership position. People high in SDO were more likely to obtain leader positions than to obtain follower positions. No other effects were significant. Second, leaders high in SDO partnered with an agreeable (confederate) follower made decisions that were more unethical than those of leaders low in SDO. Third, followers high in RWA were more acquiescent to and supportive of an unethical (confederate) leader than were followers low in RWA. Fourth, high SDO leader-high RWA follower dyads made decisions that were more unethical than those made in role-reversed dyads because leaders had more influence. Implications of these results for conceptualizing SDO, RWA, and authoritarian dynamics are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)