Limits of visual acuity in the frontal field of the rock pigeon (Columba livia)

The eye of the rock pigeon is typical of a granivorous lateral-eyed bird, in that it has both a laterally projecting central fovea and a second high-density cellular area in peripheral retina (area dorsalis) which projects to the binocular frontal field below the beak. Such a dual system is faced with potentially different optical restraints arising from central and peripheral vision. We asked whether the frontal axis can support high resolution vision from a refractive resting position (predicted to be 25-33 cm; Fitzke et al, 1985 Journal of Physiology 369 33-44) to some near point of accommodation. We measured the visual acuity on the frontal axis in five pigeons using an operant discrimination of high-contrast square-wave gratings at a series of distances from 7 to 80 cm from the eye. The peak average acuity was 11.04 cycles deg(-1), which occurred 10 cm from the eye. The average of the maximum acuity of each bird at 10 cm was 12.8 +/- 1.1 cycles deg(-1), a value equal to the Nyquist frequency calculated from the peak ganglion cell density of the area dorsalis. However, this maximum acuity was restricted to a narrow depth in space, located around 10 cm from the eye, and at greater distances fell exponentially such that acuity was 50% of its maximum at 35 cm and less than 1 cycle deg(-1) at 100 cm. We propose that the range of high-acuity vision is limited in the frontal field by either increased refractive power and/or inaccuracy in frontal accommodation, and is optimized for a preferred far point located 10 cm from the eye.     

Understanding how speed affects performance of polyrhythms: transferring control as speed increases

Pianists (N = 9) memorized and performed polyrhythms over a range of speeds from 1 to 16 notes/s. Using several fingers of each hand to press the keys on a piano keyboard, they performed the 5:3 polyrhythm by playing "3s" with one hand simultaneously with "5s" in the other. All the participants were able to maintain overall tempos and rhythms to within 10% of target speeds despite increasing difficulty. Increasing speed led to a transfer of control at about 6 notes/s, with a modular system operating above that speed. The participants were also able to engage in timing coupling at all speeds, even when the hands belonged to different people.     

Motor imagery vividness and symptom severity in Parkinson's disease

Motor imagery (MI), the mental simulation of movement in the absence of overt motor output, has demonstrated potential as a technique to support rehabilitation of movement in neurological conditions such as Parkinson's disease (PD). Existing evidence suggests that MI is largely preserved in PD, but previous studies have typically examined global measures of MI and have not considered the potential impact of individual differences in symptom presentation on MI. The present study investigated the influence of severity of overall motor symptoms, bradykinesia and tremor on MI vividness scores in 44 individuals with mild to moderate idiopathic PD. Linear mixed effects modelling revealed that imagery modality and the severity of left side bradykinesia significantly influenced MI vividness ratings. Consistent with previous findings, participants rated visual motor imagery (VMI) to be more vivid than kinesthetic motor imagery (KMI). Greater severity of left side bradykinesia (but not right side bradykinesia) predicted increased vividness of KMI, while tremor severity and overall motor symptom severity did not predict vividness of MI. The specificity of the effect of bradykinesia to the left side may reflect greater premorbid vividness for the dominant (right) side or increased attention to more effortful movements on the left side of the body resulting in more vivid motor imagery.     

Persistence,change, and explanation

I would like to express my deepest gratitude to George Myro for his wonderful insight, advice, and support, in writing this paper. I would also like to thank Ermanno Bencivenga, John Broome, Janet Broughton, Alan Code, Paul Grice, Mark Johnston, David Lewis, Paul Kube, Dugald Owen, Steve Yablo, and Colloquium participants at University of Virginia and Ohio State University for their very helpful discussions.     

The birth and death of religious leaders

The phenomenon of religious leadership is a complex one. This article proposes that Ernest Becker's insight into the human tendency to deny death contributes to a better understanding of both the psychological and sociological dimensions of religious leadership. Specifically, it examines the role of transference in the leader-follower relationship and probes how this mechanism promotes the birth and demise of religious leaders. Some practical suggestions for healthy leader-follower relations are offered.     

Use of a common software system for collaborative clinical research on attentional processes in schizophrenia and ADHD

MacArthur Network III, consisting of five nodes (locations) and over 100 investigators, was formed in 1983 to conduct collaborative clinical research on risk and protective factors associated with psychiatric disorders. The common measurement of attentional dysfunction associated with two specific disorders (schizophrenia and attention deficit-hyperactivity disorder) was a goal of a subgroup of 11 Network III investigators. In this paper, the experiences with five approaches for implementing common protocols on laboratory computers for collaborative clinical research are described. The reasons for selecting the approach provided by Schneider’s (1988) MEL system are presented and discussed.     

The influence of peers on children''s judgments about engaging in behaviors that threaten their safety

Unintentional injuries are the number one cause of death among children beyond one year of age. Many injuries among school-age children happen when they are away from home and in the company of peers. The aim in this study was to examine peer influences on children's judgments about engaging in behaviors that threaten their physical safety. Children were shown pictures depicting play situations which involved different paths of travel, each of which posed different degrees of injury risk. Children were asked to select the path they would take, and to assign a danger rating to reflect their beliefs about the likelihood of injury along this path. A peer-influence session followed, in which a same-sex friend attempted to persuade the child to take another path. Following exposure to the friend's arguments, children made their final decision about a path of travel in each play situation; the peer was not present during this decision and the experimenter present was unaware of the child's initial path choice. A number of other measures were taken in an effort to determine factors that influence children's risk-taking decisions. Results revealed that friends were successful in their persuasion efforts: for two of the three play situations, a significant number of children who initially selected low-risk paths switched to more risky paths. Appraisal of danger related to initial path decisions, but number of hazards identified and injury history did not significantly relate to initial decisions. The implications of these results for our understanding of injury-outcome processes are discussed.     

Who remembers best? Individual differences in memory for events that occurred in a science museum

Individual differences in memory and suggestibility were assessed in an experiment involving 1989 people who attended the Exploratorium, a science museum located in San Francisco. Subjects watched a brief film clip of an assault and later answered questions about it. Approximately half received misinformation about some critical items. Four demographic variables (gender, educational level, age, and occupation) were examined to determine their impact on memory performance. The principle of discrepancy detection predicts that, compared to individuals with a good memory, people who have poor memory to begin with will be relatively suggestible (that is susceptible to misinformation). Some of our findings were consistent with this principle. For example, children (5–10 years) and elderly (over 65) were relatively inaccurate and also relatively suggestible. Other findings were not consistent with the principle, for example the finding that artists and architects were relatively accurate, but they were also highly suggestible.     

Hemispheric specialization for speech opposed,by contralateral noise

Twenty right-handed Ss listened to a dichotic tape in which one of six consonant-vowel syllables was paired with a burst of white noise on each trial. Eight blocks of 40 trials were presented, with the syllables within a block presented to, the same ear. On each trial, Ss decided if/ ba/ was presented. Mean RT to right-ear items was 440.0 msec, while mean left-ear RT was 453.6 msec. Responses indicating the presence of /ba/ were made significantly more quickly than responses indicating its absence, with no significant interaction of ear and type of decision. This study demonstrated a right-ear advantage in the perception of spoken syllables when noise is presented to the opposite ear. An interpretation of the RT differences between ears in terms of callosal transmission time is discussed, and implications of this study for the perceptual origins of the ear advantage effect are considered.