Mate choice and friendship in twins: evidence for genetic similarity

This study examined the genetic and environmental contribution to people's preference for spouses and friends to be similar to themselves. In their responses to 130 personality, attitude, and demographic questions, 174 pairs of monozygotic (MZ) twins resembled each other (r= .53) more than did 148 pairs of dizygotic (DZ) twins (r= .32), 322 pairs of spouses (r= .32), and 563 pairs of best friends (r= .20). It was not previously recognized that spouses and friends are as similar as DZ twins. MZ twins also chose spouses and best friends more similar to their co-twins' friends and spouses than did DZ twins (mean rs = .22 vs. .14). The twins' preference for spouses and friends similar to themselves was about 34% due to the twins' genes, 12% due to the twins' common environment, and 54% due to the twins' unique (nonshared) environment. Similarity to partners was more pronounced on the more heritable items than the less heritable items. It is concluded that people are genetically inclined to choose as social partners those who resemble themselves at a genetic level.     

Referential processing: Reciprocity and correlates of naming and imaging

To shed light on the referential processes that underlie mental translation between representations of objects and words, we studied the reciprocity and determinants of naming and imaging reaction times (RT). Ninety-six subjects pressed a key when they had covertly named 248 pictures or imaged to their names. Mean naming and imagery RTs for each item were correlated with one another, and with properties of names, images, and their interconnections suggested by prior research and dual coding theory. Imagery RTs correlated .56 (df = 246) with manual naming RTs and .58 with voicekey naming RTs from prior studies. A factor analysis of the RTs and of 31 item characteristics revealed 7 dimensions. Imagery and naming RTs loaded on a common referential factor that included variables related to both directions of processing (e.g., missing names and missing images). Naming RTs also loaded on a nonverbal-to-verbal factor that included such variables as number of different names, whereas imagery RTs loaded on a verbal-to-nonverbal factor that included such variables as rated consistency of imagery. The other factors were verbal familiarity, verbal complexity, nonverbal familiarity, and nonverbal complexity. The findings confirm the reciprocity of imaging and naming, and their relation to constructs associated with distinct phases of referential processing.     

The relative contributions of predictiveness and salience in flavor aversion learning

Two experiments investigated the relative influence of cue predictiveness and stimulus salience on flavor aversion learning. In the first study experimental subjects experienced a nonsalient strawberry flavor and a different, more salient flavor prior to illness on each of the first three conditioning trials; the nonsalient strawberry and salient lemon were paired with illness on the fourth trial. This treatment resulted in a strong aversion to the strawberry flavor and on aversion to the lemon flavor. In contrast, animals which had experienced only a single pairing of strawberry, lemon, and illness acquired a strong aversion to lemon and no aversion to strawberry, while animals which had experienced only the pairing of different flavors and illness on each of the first three trials developed a strong aversion to both strawberry and lemon. Experiment 2 replicated the results of the experimental condition of the first study but also included a “blocking” condition in which subjects received three strawberry and illness pairings prior to a strawberry-lemon-illness pairing. Subjects in the blocking condition developed only a weak aversion to strawberry, and this aversion did not block the development of a strong lemon aversion. Apparently, in order for a nonsalient flavor cue to block the acquisition of an aversion to a more salient cue, the nonsalient flavor must not only be paired with illness but also be more predictive of illness than the more salient flavors also paired with illness. The data were discussed in terms of the R. A. Rescorla and A. R. Wagner's associative model (1972, in Classical conditioning II: Current research and theory, New York: Appleton-Century-Crofts), R. A. Rescorla's catalytic model (1982, Journal of Experimental Psychology: Animal Behavior Processes,8, 131–141), and N. J. Mackintosh's attentional model (1975, Psychological Review,82, 276–298) of conditioning.     

Discrimination without awareness?

The fate of the unattended message in dichotic listening experiments is a much disputed issue. Moray (1969) proposes that there is no processing of the unattended message, whereas Norman (1969) has suggested that it is analyzed to the level of meaning. In order to test these alternative hypotheses an experiment was performed in which galvanic skin responses (GSR) were conditioned to a word (CS) by pairing it with shock. The word was then included in passages of prose presented to subjects as the attended and unattended messages in a dichotic listening task. GSR's were obtained to the occurrence of CS in the unattended message and also to words acoustically similar to CS and to synonyms of CS. The probability of obtaining a GSR to the occurrence of an accoustically similar word was increased by placing that word in a context appropriate to CS. These results suggest that the unattended message can be processed to a level at which semantic information is extracted without the subject's reported awareness.     

The genetics and evolution of the general factor of personality

Three studies tested the hypothesis that a general factor of personality (GFP) underlies diverse individual differences including altruism, the Big Five factors of Openness, Conscientiousness, Extraversion, Agreeableness, and Emotional Stability, and the EAS temperament traits of Emotional Stability, Activity, and Sociability. In Study 1, 214 university students completed 36 personality scales. In Study 2, 322 pairs of monozygotic (MZ) and dizygotic (DZ) twins completed 29 5-point rating scales plus questionnaires. In Study 3, 575 pairs of 2- to 9-year-old Korean twins were rated by their mothers on 25 temperament scales. Factor analyses revealed a hierarchical organization with GFP at the apex and the Big Five and/or EAS temperament scales intermediate. The twin data show GFP has an early age of onset with 50% of the variance attributable to non-additive (dominance) genetic influence and 50% to unique, non-shared environmental influence. We discuss a life history matrix encompassing brain size, maturational speed, and longevity, plus emotional intelligence and the personality disorders, and suggest natural selection acted directionally to endow people with more cooperative and less contentious personalities than their archaic ancestors, or nearest living relatives, the chimpanzees.     

Revised norms for the Lollipop Test for children ages 42 to 65 months

Lollipop Test scores were acquired for 1,402 preschoolers in southwestern Indiana. Means and standard deviations for both boys and girls by 6-mo. intervals from the ages of 42 through 65 months showed scores increased significantly across ages, with girls scoring significantly higher than boys in all age groups. Current mean scores are similar to those published in 1988 for boys and slightly higher for girls.     

Spatial contrast sensitivity does not explain random figure discrimination latency

Both humans and other mammals can more easily discriminate eight-sided figures from one another than they can figures having more or fewer sides. The hypothesis that this effect is based upon spatial contrast sensitivity was tested by varying viewing distance and hence spatial frequency content. Because viewing distance had tittle effect upon relative discrimination latency, it was concluded that the superior discriminability of eight-sided figures is not based upon spatial contrast sensitivity. The possibility that orientation tuning of visual cortex neurons may account for the effect is discussed.