Stimulus generalization: the ordering and spacing of test stimuli

Twenty-four pigeons learned a successive discrimination between 500 mmu (S+) and 574 mmu (S-). When tested in extinction, some birds received stimuli around S+, with no S- presentations. These birds showed a positive peak shift, with maximum responding not at 550 mmu, but displaced to 538 mmu and 544 mmu. Other birds were tested with stimuli around S-, with no S+ presentations. These birds showed a negative shift, with least responding not at 574 mmu, but at 586 mmu. Though the first group was tested around S+ and the second around S-, total responding between groups did not differ. When retested on the other half of the continuum, however, birds that had gone from the S+ half to the S- half responded fewer times than those that had gone from the S- half to the S+ half. In a second experiment, reducing stimulus spacing from 6 mmu to 2 mmu produced flatter gradients and decreased the amount of positive shift. In a third experiment, birds were tested across the whole continuum with stimuli presented in serial order. A sequence from 538 mmu to 586 mmu produced no responding after the first part of the session; a sequence from 586 mmu to 538 mmu produced responding throughout the session.     

Infant psychiatry clinic grand rounds. Unresolved grief: A two-year-old brings her mother for treatment

Rebecca was a 2 ¹/₂ -year-old Caucasian female who was brought to the Infant Psychiatry Clinic by her 28-year-old widowed mother. Her mother's chief concern was around parenting issues as well as how to explain to Rebecca the death of her father. This loss occurred when Rebecca was 6 months old and was a source of great pain and unresolved grief to her mother. Central to this case was the chaotic history of Rebecca's mother, who was a victim of incest from the time she was 13 until she was 23 years old. Both of her parents struggled with chronic alcoholism during much of her childhood. It appeared that a factor precipitating the mother's request for help was her struggle to move out of her own mother's home. This outpatient Infant Clinic case involved two primary goals: (1) the assessment of the parent-child relationship and (2) the development of confidence in this “good enough” mother. Vitally important to the process of treatment was the mother's modulation of timing and frequency of sessions. The issue of pacing was carefully monitored as this mother could have been overwhelmed by delving precipitously into her incestuous history. The use of a structured videotape interview to address mother-child interaction and parenting issues was particularly helpful. Referral to an AlAnon group provided the mother with social support as she separated herself from her alcoholic mother and moved toward autonomy in her own parenting role.     

Effects of Age on the Generalization and Incubation of Memory in the F344 Rat

Freezing (immobility) in the presence of aversive stimuli is a species-specific behavior that is used as an operational measure of fear. Conditioning of this response to discrete sensory stimuli and environmental context cues has been used as a tool to study the neuropsychology of memory dynamics and their development over the lifespan. Three age groups of F344 rats (3, 9, and 27 month) received tone–foot shock pairing (or tone only) in a distinctive chamber on two consecutive days. Separate subgroups of rats from each age group were then tested, at retention intervals of 1, 20, 40, or 60 days, for context-mediated fear in the environment in which they were trained, for generalization of the fear response to a novel chamber, and for fear of the tone. Beginning at day 20, the 27-month-old rats exhibited less freezing behavior than did younger rats when tested in the conditioning context. This age difference was a result of freezing behavior becoming progressively stronger with time in the two younger age groups, a phenomenon that has been referred to as memory incubation. Incubation of the contextual fear response was not detected in the old rats. In a novel context, all age groups exhibited significantly more freezing than did control animals. There was also pronounced incubation of this generalized freezing response, and the extent of incubation declined significantly with age. In the novel context, the freezing response to the tone was robust in all age groups and increased over time, in constant proportion to the degree of freezing elicited by the novel context itself, prior to tone onset. The fact that old animals are known to be relatively selectively impaired in forms of memory that depend on a functional hippocampus suggests a possible explanation for the reduced incubation effects seen in old rats; however, whether the increased expression of fear over time is mediated by a hippocampal-dependent memory consolidation process or whether it reflects a generalized increase in the gain of the circuitry mediating the fear response itself, remains to be determined.     

Bias to experience approaching motion in a three-dimensional virtual environment

We used two-frame apparent motion in a three-dimensional virtual environment to test whether observers had biases to experience approaching or receding motion in depth. Observers viewed a tunnel of tiles receding in depth, that moved ambiguously either toward or away from them. We found that observers exhibited biases to experience approaching motion. The strengths of the biases were decreased when stimuli pointed away, but size of the display screen had no effect. Tests with diamond-shaped tiles that varied in the degree of pointing asymmetry resulted in a linear trend in which the bias was strongest for stimuli pointing toward the viewer, and weakest for stimuli pointing away. We show that the overall bias to experience approaching motion is consistent with a computational strategy of matching corresponding features between adjacent foreshortened stimuli in consecutive visual frames. We conclude that there are both adaptational and geometric reasons to favor the experience of approaching motion.     

The development of phonological awareness in preschool children

A short-term longitudinal study was carried out on a group of 67 preschool children. At three points in time over a 12-month period, the children were given tests measuring their syllable, rime, and phoneme awareness, speech and language skills, and letter knowledge. In general, children's rime skills developed earlier than their phoneme skills. Structural equation models showed that articulatory skills and syllable and rime awareness predicted later phoneme awareness.     

Relating the perception of visual ensemble statistics to individual levels of autistic traits

Integrating information across the visual field into an ensemble (e.g., seeing the forest from the trees) is an effective strategy to efficiently process the visual world, and one that is often impaired in autism spectrum disorder. Individual differences in sensory processing predict ensemble encoding, providing a potential mechanism for differing perceptual strategies across individuals, and possibly across diagnostic groups exhibiting atypical sensory processing. Here, we explore whether ensemble encoding is associated with traits associated with autism spectrum disorder (ASD). Participants (N=68) were presented with an ensemble display consisting of circles of varying sizes and colors, and were asked to remember the size of the red and blue circles, while ignoring the green circles. Participants were then cued to a target location after a brief delay, and instructed to report the remembered size of the circle they had previously viewed in that location, as ensemble information commonly biases memory for individual objects toward the probed mean of a set of similar objects. The Autism-spectrum Quotient (AQ) was completed to measure each individual’s level of autistic traits. We found that an individual’s level of ensemble perception, measured as their bias toward the probed mean, was negatively associated with a higher level of ASD traits. These results suggest that individuals with higher levels of ASD traits are less likely to integrate perceptual information. These findings may shed light on different perceptual processing within the autism spectrum, and provide insight into the relationship between individual differences and ensemble encoding.