Extraction of relief from visual motion

We quantified the ability of human subjects to discriminate the relative distance of two points from a slanted plane when viewing the projected velocities of this scene (orthographic projection). The relative distance from a plane (called relief) is a 3-D property that is invariant under linear (affine) transformations. As such, relief canin principle be extracted from the instantaneous projected velocity field; a metric representation, which requires the extraction of visual acceleration, is not required. The stimulus consisted of a slanted planeP (specified by three points) and two pointsQ ₁ andQ ₂ that are non-coplanar withP. This configuration of points oscillated rigidly around the vertical axis. We have measured thesystematic error andaccuracy with which human subjects estimate the relative distance of pointsQ ₁ andQ ₂ from planeP as a function of the slant of_P. The systematic error varies with slant: it is low for small slant values, reaches a maximum for medium slant values, and drops again for high slant values. The accuracy covaries with the systematic error and is thus high for small and large slant values and low for medium slant values. These results are successfully modeled by a simple relief-from-motion computation based on local estimates of projected velocities. The data are well predicted by assuming (1) a measurement error in velocity estimation that varies proportionally to velocity (Weber’s law) and (2) an eccentricity-dependent underestimation of velocity.     

年龄、作业难度和训练对成人记忆的影响

采用“联想学习”、“图象自由回忆”和“附加联想”三项目,对９０例成人（分为青年、老年和老老年组各３０例）进行记忆测查和训练,目的为探讨年龄,作业难度和训练对记忆的影响。结果表明：青年组记忆成绩明显高于老年和老老年组,后两组无显著差异;无关联想的年龄差异大于有关联想,作业难度扩大了年龄差异;各年龄组训练后记忆得到明显改善,并且训练扩大了年龄和作业易难的差异。由此可见,记忆受年龄、作业难度和训练三因素的相互作用,也再次证实了老年认知功能具有一定的可塑性。     

Are microsaccades responsible for the gap effect?

Extinguishing a fixation point shortly before, or concurrently with, the onset of a peripheral visual target reduces the latency of saccades to that target. Saslow (1967) hypothesized that thisgap effect might occur because fixation point offsets reduce the incidence of corrective microsaccades with an associated saccadic refractory period. In the present study, a robust gap effect was obtained. However, using a Purkinje image eyetracker with 1 arcmin of resolution, we found that fixation point offsets had no effect on the occurrence of microsaccades and that the occurrence of microsaccades had no impact on the magnitude of the gap effect. Microsaccades therefore do not appear to play any part in the production of the gap effect.     

Book reviews

Integrative Psychological and Behavioral Science -     

An affordable computer-aided method for conducting Morris water maze testing

A relatively inexpensive and reliable computer-aided method for assessing Morris water maze performance is described. The procedure uses SigmaScan digitizing software (Jandel Scientific, San Rafael, CA) to collect distance swum data, while escape latencies are measured with a hand-held stopwatch. Swim paths are videotaped for subsequent viewing and saved on disk as data sets ofx,y coordinates. At a later time,x,y data files are printed and analyzed to obtain additional performance measures (e.g., distance swum in previous reinforced quadrant, heading angle, etc.). Intra- and interrater reliabilities associated with this method are presented. Correlation coefficients in ther = .85?.90 and above range are reported for both reliability types. Given its approximate cost of $1,500 (excluding the price of an IBM-compatible computer), the present procedure potentially can aid in performing instructional and research activities at small colleges which typically lack extensive equipment budgets.     

Aggressivity,inattention, hyperactivity,and impulsivity in boys at high and low risk for substance abuse

Aggressivity, inattention, hyperactivity, and impulsivity are cardinal dimensions of externalizing behavior problems of childhood. They are diagnostic and clinical features of childhood disorders, and are thought to be linked to the subsequent development of adult disorders such as substance abuse (SA). Little is known, however, about the convergent and discriminant validity of these four constructs. We used multiple measures to develop indices of aggressivity, inattention, hyperactivity, and impulsivity in a sample of 10- to 12-year-old boys (N=183) with and without a family history of SA. Data were taken from mother reports, child reports, teacher reports, and laboratory tasks. The study aims were (1) to test the convergent and discriminant validity of aggressivity, inattention, hyperactivity, and impulsivity; (2) to examine whether the data were consistent with a model specifying the four constructs as indicators of one superordinate factor; and (3) to differentiate boys with and without a family history of SA in construct scores. The results supported the convergent and discriminant validity of the four constructs. Although discriminable, the constructs covaried strongly and were consistent with a model specifying them as indicators of a single superordinate factor. Boys with a family history of substance abuse scored higher than control boys on aggressivity, inattention, and impulsivity scores, but the groups did not differ on hyperactivity scores. The results are discussed in terms of the role of childhood behavior problems in vulnerability to SA.This work was supported by the National Institute on Drug Abuse grant No. DA 05605.     

The mediating role of anxiety in self-reported somatic complaints of depressed adolescents

This study examined the mediating role of anxiety in the self-reports of somatic complaints in 96 depressed adolescent inpatients. Sixty-four subjects with major depressive episodes and comorbid anxiety disorders (MDE-A) determined from the Diagnostic Interview for Children and Adolescents-Revised (DICA-R) reported significantly more somatic complaints than 32 adolescents having major depressive episodes without comorbid anxiety (MDE). An analysis of covariance demonstrated that, with anxiety symptoms controlled, MDE and MDE-A groups did not differ significantly in somatic complaints. A hierarchical multiple-regression analysis revealed that, with demographic and anxiety symptoms controlled, depressive symptoms did not contribute to the explanation or prediction of somatic complaints. The results suggest that anxious, but not depressive symptoms, are independently associated with somatic complaints. The results are discussed in light of new affective models of psychopathology.     

Selectively prompting speech repairs in stages I to V: A technique for investigating early metalinguistic abilities

When children aged from 1;6 to 3;6 made errors in relation to targeted morphemes within grammatically obligatory contexts, a prompt of “Pardon?” was given. Morpheme repair rates increased with linguistic proficiency, and with target morpheme mastery. The selective use of prompted repairs appears to be a useful technique for assessing rudimentary abilities to monitor grammatical form within very young children.     

Controlled attention sharing influences time estimation

A seminal attentional model of time estimation predicts that subjective duration will be positively correlated to the amount of attention given to temporal processing. This prediction holds under prospective conditions, in which one is forewarned that judgments of time will be asked, in contrast to retrospective conditions, in which such judgments are required after the relevant period without any prior warning. In three experiments, an attention-sharing method was used. Subjects were asked to control the amount of attention that they devoted to one or the other component of a dual-task paradigm. The first experiment involved word categorization and reproduction of duration. The following experiments, based on signal detection theory, required discrimination of both the duration and the intensity of a single stimulus, in the visual (Experiment 2) or the auditory (Experiment 3) modality. The results indicate that when the attention is directly controlled by the subject, the subjective duration shortens as the amount of attention devoted to the temporal task diminishes. The implications of these results for the possible existence of an internal timer are considered.