Illusory changes in a sound source and outflow theory.

Two experiments, with a total of 220 Ss, were conducted to investigate the possibility of illusory movement of a sound source. In Experiment 1 intensity level (from 10 to 60 db SPL) and frequency of an auditory sound (from 1000 to 5000 Hz) were varied while the Ss head was stabilized with a head rest; in Experiment 2, intensity and frequency were also varied while the S's head was free to move. When head position was fixed, error signal variables such as intensity had no effect on the frequency of illusory direction changes of a sound source. However, when the head position was not fixed, increasing the intensity of the sound source significantly decreased the number of reported illusory direction changes. In addition, in both experiments, illusory changes of intensity were experienced by Ss, and increasing the intensity of the sound source also decreased this illusion. The results were interpreted in the context of an error signal and noise model of autokinetic effects, and the implications for the perception of auditory localization and movement of a sound source were discussed.

Gender and energy balance: sex differences in adaptations for feast and famine.

According to this theory/review, the cross-culturally common finding of more women than men among the obese is at least in part a consequence of sex differences in evolutionary selection pressure. James and Trayhurn claim that the propensity to obesity is linked to th ability to survive a fast and both may involve reduced heat production. The present theory extends this relationship to sex differences in energy balance. According to the theory proposed here, mammalian females were subjected to more severe selection pressures during times of short food supply than males were and hence females were under more pressure to evolve mechanisms to facilitate survival during famine, which led to sex differences in obesity. The data relevant to sex differences in starvation survival, obesity and heat production, and the possible evolutionary roles and implications of sex differences in chromosomes and in organizational and activational sex hormones are reviewed. The conclusion is that evolution has created a linkage between sex chromosomes, hormones and energy balance, and this linkage is at least in part responsible for the greater resistance of the female to famine and for her greater tendency to become obese in times of feast.

Sex differences in the perception of autokinetic movement of an afterimage.

The effects of stimulus color and gender upon the perception of an afterimage were examined. The Ss were 32 male and 32 female college undergraduate volunteers. Eight Ss of each gender viewed a pinpoint flash of light through one of four filters: blue-green (Wratten 44A), red (Wratten 92), yellow (Wratten 9), or a neutral (Wratten 96) filter. Each S was given three trials, and on each trial, the duration of the afterimage was recorded, along with changes of direction, and changes in perceived color. Males reported significantly (p less than .05) more autokinetic movement of the afterimage. The color of the stimulus affected afterimage duration differentially for the two genders (p less than .05), and there was also a significant interaction (p less than .02) of gender with filter color for the total number of color changes reported. Thus, it is likely that both outflow monitoring and error signal variables in the autokinetic effect may be affected by gender, and the two sexes may also have different retinal and/or central processing of visual information.

Autokinetic movement of an induced afterimage.

Thirty-two female Ss participated in an experiment in which autokinetic movement (AKM) direction change frequency of an induced afterimage was assessed as a function of stimulus afterimage color (yellow or blue-green) and the presence or absence of eye strain. Afterimage color was found not to affect AKM frequency reports. However, eye strain significantly (p less than .002) affected such reports, with the fewest AKM direction changes reported when strain was present. These results were explained in terms of an error signal and noise analysis of AKM.

Prismatically induced eye strain and autokinetic direction frequency.

Autokinetic movement (AKM) as assessed by number of reported direction changes was evaluated for 25 college sophomores as a function of prism displacement strength. The results indicated that the strain on the eye muscles produced by prism displacement significantly affected frequency of direction change reports: the greater the displacement, the fewer the number of reported direction changes. These results were interpreted according to outflow theory in terms of the prism-imposed strain effectively increasing the level of noise in the outflow monitoring system, thereby making the detection of a cancelling response signal, the direction change, more difficult.

Effects of stimulus size, intensity, color, and eye strain on autokinetic movement: an error signal and noise analysis.

In two experiments, with a total of 116 male and female undergraduate S s, predictions were tested from the following hypothesized explanation of autokinetic movement (AKM): undetected eye drifts lead to movement of the AKM target across the retina; this movement or error signal leads to the initiation of a cancelling response, and the AKM is directly due to CNS monitoring of the efferent responses or signals sent to the eye muscles with subsequent detection of these signals against a background of efferent noise. The error signal variables studied were stimulus color (yellow or blue-green), stimulus intensity (dim or bright), and stimulus size (1.0 or .1 deg visual angle). Small, dim lights foveally viewed and yellow as opposed to blue-green lights led to significantly more error signals and hence more AKM as measured by mean number of perceived direction changes. Also, increasing retinal displacement by changing viewing angle (from zero to 60 deg) or increasing displacement by increasing diopter strength of prisms (from zero to 30) decreased AKM as measured by number of direction changes, and this effect is due at least in part to the increase in efferent noise caused by the increases in eye muscle tension involved. It was concluded that retinal displacement affects both error signal and noise variables in the AKM and, presumably, in the perception of real movement as well.

Outflow theory and autokinetic movement: color, viewing angle, and dark adaptation.

The number of reported changes in direction of autokinetic movement was assessed as a function of color of the light that served as stimulus, viewing angle (0, 30, or 60 deg of displacement from straight ahead), and dark adaptation. Color and dark adaptation had no significant main effect on the number of reported changes in direction for the red and yellow lights, but viewing angle was inversely related to the number of reported changes. For the blue-green light, atypical effects of viewing angle and dark adaptation were found.