Failure of hierarchical conditional rule learning in the pigeon (Columba livia)

Pigeons were trained with a conditional discrimination task in three-key operant chambers. Choosing either the left or right key was followed by food according to combinations of three preceding events: (a) a houselight illumination condition (dark or light), (b) presence or absence of green flashes on the three keys, (c) a color (amber or blue) of the center sample key. With these 2×2×2 event combinations, eight types of correct trials were prepared: (1) dark→no flash→amber→LEFT, (2) dark→no flash→blue→RIGHT, (3) dark→flash→amber→RIGHT, (4) dark→flash→blue→LEFT, (5) light→no flash→amber→RIGHT, (6) light→no flash→blue→LEFT, (7) light→flash→amber→LEFT, and (8) light→flash→blue→RIGHT. Seven of these eight types were used for training of a given bird, and then the remaining trial type was presented as the test. If the birds had learned the conditional structure of the events (the hierarchical switching rule), they would have responded correctly to the test type. However, they chose the opposite side key, suggesting that they had learned cue configuration or multiple rules to solve the task. Accepted after revision: 13 January 2001 Electronic Publication     

Mediated configural learning in rats

Three experiments investigated mediated configural learning in male rats. In Experiment 1, after exposure to audio-visual compounds AX and BY, rats received trials where X was paired with shock, and Y was not. The idea that conditioning with X enables the evoked configural representation of AX to be linked to shock received support from the facts that while AX provoked more fear than BX, there was no difference between BY and AY. Similarly, Experiment 2 showed that after exposure to AX and BY, separate pairings of X and Y with shock resulted in more fear to AX and BY than AY and BX. In Experiment 3, rats in group consistent received separate exposures to A and X in Context C, and B and Y in D, while those in group inconsistent received A and X (and B and Y) in both C and D. After rats had received shocks in both C and D, rats in group consistent showed more fear to AX and BY than to BX and AY, but this was not the case in group inconsistent. These results indicate that configural representations, formed either by presenting auditory and visual stimuli as parts of a compound or in a shared context, are subject to a process of mediated learning.     

The role of comparison in preschoolers’ novel object categorization

We examined the role of the comparison process and shared names on preschoolers’ categorization of novel objects. In our studies, 4-year-olds were presented with novel object sets consisting of either one or two standards and two test objects: a shape match and a texture match. When children were presented with one standard, they extended the category based on shape regardless of whether the objects were named. When children were presented with two standards that shared the same texture and the objects were named with the same noun, they extended the category based on texture. The opportunity to compare two standards, in the absence of shared names, led to an attenuation of the effect of shape. These findings demonstrate that comparison plays a critical role in the categorization of novel objects and that shared names enhance this process.     

Facelikeness matters: A parametric multipart object set to understand the role of spatial configuration in visual recognition

There is a view that faces and objects are processed by different brain mechanisms. Different factors may modulate the extent to which face mechanisms are used for objects. To distinguish these factors, we present a new parametric multipart three-dimensional object set that provides researchers with a rich degree of control of important features for visual recognition such as individual parts and the spatial configuration of those parts. All other properties being equal, we demonstrate that perceived facelikeness in terms of spatial configuration facilitated performance at matching individual exemplars of the new object set across viewpoint changes (Experiment 1). Importantly, facelikeness did not affect perceptual discriminability (Experiment 2) or similarity (Experiment 3). Our findings suggest that perceptual resemblance to faces based on spatial configuration of parts is important for visual recognition even after equating physical and perceptual similarity. Furthermore, the large parametrically controlled object set and the standardized procedures to generate additional exemplars will provide the research community with invaluable tools to further understand visual recognition and visual learning.     

Perception of shape from shading in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

The perception of shape from shading was tested in two chimpanzees (Pan troglodytes) and five humans (Homo sapiens), using visual search tasks. Subjects were required to select and touch an odd item (target) from among uniform distractors. Humans found the target faster when shading was vertical than when it was horizontal, consistent with results of previous research. Both chimpanzees showed the opposite pattern: they found the target faster when shading was horizontal. The same difference in response was found in texture segregation tasks. This difference between the species could not be explained by head rotation or head shift parallel to the surface of the monitor. Furthermore, when the shaded shape was changed from a circle to a square, or the shading type was changed from gradual to stepwise, the difference in performance between vertical and horizontal shading disappeared in chimpanzees, but persisted in humans. These results suggest that chimpanzees process shading information in a different way from humans. Received: 20 January 1998 / Accepted after revision: 30 March 1998     

Statistical evaluation of measures of fit in the Lingoes-Borg procrustean individual differences scaling

PINDIS, as recently presented by Lingoes and Borg [1978] not only marks the latest development within the scope of individual differences scaling, but, may be of benefit in some closely related topics, such as target analysis. Decisions on whether the various models available from PINDIS fit fallible data are relatively arbitrary, however, since a statistical theory of the fit measures is lacking. Using Monte Carlo simulation, expected fit measures as well as some related statistics were therefore obtained by scaling sets of 4(4)24 random configurations of 5(5)30 objects in 2, 3, and 4 dimensions (individual differences case) and by fitting one random configuration to a fixed random target for 5(5)30 objects in 2, 3, and 4 dimensions (target analysis case). Applications are presented.     

Influence of shape on haptic curvature perception

Curvature discrimination of hand-sized doubly curved surfaces by means of static touch was investigated. Stimuli consisted of hyperbolical, cylindrical, elliptical and spherical surfaces of various curvatures. In the first experiment subjects had to discriminate the curvature along a specified orientation (the discrimination orientation) of a doubly curved surface from a flat surface. The curvature to be discriminated was oriented either along the middle finger or across the middle finger of the right hand. Independent of the shape of the surface, thresholds were found to be about 1.6 times smaller along the middle finger than across the middle finger. Discrimination biases were found to be strongly influenced by the shape of the surface; subjects judged a curvature to be more convex when the perpendicular curvature was convex than when this curvature was concave. With the results of the second experiment it could be ruled out that the influence of shape on curvature perception was simply due to a systematic error made by the subject regarding the discrimination orientation.     

Demonstration of the shape bias without label extension

Existing shape bias research has determined that children generally extend object labels to novel instances on the basis of shape, and this typically occurs by around age 2.5. This research was conducted to further examine the nature of this bias during the second year of life, and determined that by using a more sensitive measure (novelty preference looking time) an emerging shape bias can be found as early as 14 months of age. In addition, demonstration of the shape bias in the current experiment appears to be unrelated to the 50 count noun marker.     

Comparing the effect of haptic modalities on walking balance control: Is using one or two arms better?

BackgroundAdding haptic input by lightly touching a railing or using haptic anchors may improve walking balance control. Typical use of the railing(s) and haptic anchors requires the use of one and two arms in an extended position, respectively. It is unclear whether it is arm configuration and/or the number of arms used or the addition of sensory input that affects walking balance control.Research questionThis study examined whether using one arm or two arms to add haptic input through light touch on a railing or using the haptic anchors affects walking balance control.MethodsIn this study, young adults (n = 24) walked while using (actual use) or pretending to use (pretend use) the railing(s) and haptic anchors with one or two arms. Inertial-based sensors (Mobility Lab, APDM) were used to measure stride velocity, relative time spent in double support (%DS), and peak normalized medio-lateral trunk velocity (pnMLTV).ResultsUsing two arms lead to a decrease in pnMLTV compared to using one arm and pnMLTV was lower in the actual use trials compared to the pretend use trials for the anchors only. Stride velocity and %DS did not change between trials when one or two arms were used or when participants actually or pretended to use the haptic tools. Participants walked slower when using the railing compared to the anchors.SignificanceThe importance of considering the number of arms is highlighted in the improved balance control when using two arms with either tool. The augmented sensory input adds to the stabilizing effect of arm configuration for the anchors but not the railings. These results have implications for future research and rehabilitation efforts emphasizing sensorimotor integration to improve walking balance control.