Nonverbal cognition across genetic and environmentally informative kinships: The case for opposite-sex twin pairs and virtual twins.

The extent to which prenatal intrauterine testosterone affects cognitive development in females has been of interest. Previous twin research has, however, been limited in its attempts to disentangle prenatal and psychosocial environmental factors influencing cognitive development. The current study applied a novel approach to addressing this concern. Specifically, the nonverbal cognitive performances of female opposite-sex dizygotic co-twins (DZOSfs) and female opposite-sex virtual co-twins (same-age unrelated siblings or VTOSfs) were compared to separate the biological and environmental influences on the nonverbal IQ score and its component subtests. The DZOSf twins showed a trend toward outperforming the younger VTOSf twins on the Block Design subtest only. Using these biologically and environmentally informative kinships offers a novel approach to understanding sex differences in nonverbal cognition. Including VTOSfs as a comparison group creates an experimental design that eliminates confounds and spurious associations left unaddressed in prior twin research.

The recovery of blocked memories in repeated recall tests.

There is continued controversy over the possibility of blocked and subsequently recovered accurate memories. Memory blocking produced by a retrieval biasing procedure followed by recovery through repeated testing was demonstrated in two experiments. Predictions derived from the retrieval bias explanation and from the level of cumulative recall (LOCR) concerning hypermnesia for blocked material were tested. Expt 1 disconfirmed the retrieval bias hypothesis that the blocked material would remain blocked. However, there was no accelerated recovery despite the lower rate of recall for the bias group compared to the control group as predicted based on LOCR. Expt 2 replicated the Expt 1 findings and used metamemory tasks to further explore the recovery process. The data led the authors to conclude that accurate recovery of memory with corresponding high confidence is possible through repeated testing provided suggestive questioning and misinformation are not presented.

Effects of perceptual modality on verbatim and gist memory.

In two experiments, predictions of the fuzzy-trace theory of memory were tested. Perceptual information may play a role in retrieval and recognition processes for verbatim, but not for gist, memory. Perceptual modality effects were assessed in the present study by presenting three-sentence stories (e.g., The bird is in the cage. The cage is over the table. The bird is yellow) and then testing recognition of probes that varied on three dimensions: (1) semantic accuracy (true vs. false), (2) wording (all original words vs. one novel word included), and (3) sentence type (premise vs. inference). In Experiment 1, study modality (auditory vs. visual) was manipulated, and in Experiment 2, both study and test modalities were manipulated. Despite replicating a number of findings consistent with fuzzy-trace theory (e.g., instruction and probe type effects), the results of both experiments failed to support the idea that perceptual information plays a role in performance on verbatim memory tests.