Dynamic, state-dependent thresholds for the perception of single-element apparent motion: Bistability from local cooperativity

Previous studies have indicated that the formation of coherent patterns for multielement motion displays depends onglobal cooperative interactions among large ensembles of spatially distributed motion detectors. These interactions enhance certain motion directions and suppress others. It is reported here that perceiving one element moving between two nearby locations likewise is subject to cooperative influences (possibly facilitating and inhibiting interactions within alocal ensemble of overlapping detectors). Thresholds depending on luminance contrast were measured for a generalized singleelement apparent-motion stimulus, and evidence for spontaneous switching and hysteresis effects indicated that motion perception near the 50% threshold was bistable. That is, for conditions in which motion and nonmotion were perceived half the time, the two percepts were distinct; when one was perceived, it clearly was discriminable from the other. These results indicated that (1) single-element apparent-motion thresholds depended on the immediately preceding state of the ensemble of motion detectors responding to the stimulus, and (2) the stimulus activation of individual motion detectors always might be influenced by recurrent, cooperative interactions resulting from the detectors’ being embedded within interconnected ensembles.     

Tacit knowledge and the effect of pattern configuration on mental scanning

Two opposing hypotheses are that estimated distances may be used to predict scanning times in mental scanning experiments (Mitchell & Richman, 1980; Pylyshyn, 1981) and that scanning times may be used to estimate distances on maps (Thorndyke, 1981). We tested these hypotheses by having people both estimate lengths and mentally scan diagonal lines, spirals, and mazes. There were large and consistent differences in the rate of scanning the three configurations, regardless of whether people scanned percepts or images. These differences could not be accounted for by differences in length estimates or by people’s tacit knowledge of their scanning rates. We propose that people actually do mental scanning in a mental scanning task rather than use length estimates to generate scanning time and that they do not rely on scanning times to estimate length in a length estimation task.     

The effect of familiarity on the processing of fragmented figures

The processing of fragmented figures was investigated in a same-different reaction time task with pairs of intact and pairs of fragmented alphabet letters. The effect of fragmentation was significantly larger for pairs of letters rotated into an unfamiliar orientation than for pairs of normally oriented letters. Since this significant interaction was obtained for subjects emphasizing a structural mode of processing (Hock, 1973), it was concluded that familiarity had a direct effect on the structural/ organizational processing of the fragmented figures.     

Frequency discrimination: assessing global-level and element-level units in memory

Subjects' knowledge of how often various events occur was used to assess the retention of memory units for word-like strings of letters. A series of strings was presented at one of three exposure durations. Within the series, the frequencies of occurrence of different strings and of the letters composing the strings were varied orthogonally. At relatively long exposure durations, subjects could discriminate the frequency of occurrence for both strings and their constituent letters. The formation of global-level (string) memory units was indicated by judgments of string frequency being unaffected by either the frequencies of their component letters or experimental conditions (brief exposures) that prohibited accurate judgment of letter frequency. Although judgments of letter frequency were sometimes biased by the frequency of the strings containing the letters, the success with which the judgments discriminated different levels of letter frequency did not depend on the activation of string-level memory units. Furthermore, subjects' frequency judgments for letters were not predictable from their recall of the strings containing the letters. These results, which could not be explained by Tversky and Kahneman's (1973) "availability heuristic," provided evidence for the formation of element-level (letter) memory units. A converging experiment established that element-level frequency information could be abstracted from words as well as nonwords, and further, that this information was stored in long-term memory.     

Real-world schemata and scene recognition in adults and children

Recognition memory for previously seen multiobject scenes was examined for different types of contextual arrangements between objects in the scenes. It was found that organized scenes with novel but possible interobject relations were recognized more accurately than either organized scenes with familiar interobject relations or unorganized scenes with impossible interobject relations. This finding was obtained for adults, 8- to 10-year-old children, and 5- to 8-year-old children who indicated concrete-operational ability in Piaget’s conservation-of-liquid quantity task. The results were interpreted in conjunction with a two-stage model of scene processing involving the formation of a schema to represent a scene (Stage 1), and the operation of the schema in governing the further processing of detailed information in the scene (Stage 2). It was concluded that preoperational children can form schemata to represent organized scenes (Stage 1), but it is not until the emergence of concrete operations that these schemata become operational with respect to guiding the further processing of information in the scene (Stage 2).     

Mental rotation and perceptual uprightness

Performance in Cooper and Shepard’s (1973) mental rotation task was examined in the context of a model that defined the extent to which alphabet letters could be tilted from their normal orientation and still be perceptually upright. For letters with a broad range of orientations for which they remain perceptually upright, a nonlinear effect of orientation on reaction time was obtained (as in Cooper and Shepard). However, for letters with a narrow range of orientations for which they remain perceptually upright, reaction time was linearly related to orientation. The results supported the hypothesis that subjects in the Cooper and Shepard task would mentally rotate alphabet letters only when they were presented in orientations for which they were not perceptually upright.     

Reproducing gender in public places: Adults' attention to toddlers in three public locales

Adults of different sex interact differently with toddlers. In home and laboratory, fathers/adult males are the primary agents of sex typing and mothers/adult females are the primary caretakers, especially in the managerial aspects of child care. Little is known about the public display of childcare. Observations were made of 1588 adults (794 males and 794 females) and 1122 toddlers at: 1) a zoo, 2) an amusement park featuring rides, and 3) a theme park based on nursery rhymes. The subjects were family parties of one adult male, one adult female and one or more toddler(s). Adult males were more likely to carry toddlers and adult females were more likely to push empty strollers. Location differences were minor, as were differences in the way male and female adults interacted with toddlers of different sex. There was a toddler-of-like-sex preference in parent-toddler interaction.We wish to acknowledge the help of Michelle Dwyre, Leanne Dimungo, Tod Nirk, Bonnie Mackenzie, Sean Benedict, Keith Booth, and Lisa Dole in data collection. We are especially grateful to the staff of the Sacramento Zoo (Maria Baker, Director; Fred LaRue, former Curator of mammals; Cheryl Winn, former Education Curator and Laurie Neville and Leslie Field, Primate Department) for their encouragement. This research was supported in part by a University of California Faculty Research grant.     

Linking dynamical perceptual decisions at different levels of description in motion pattern formation: psychophysics

The relationship between local-level motion detection and higher level pattern-forming mechanisms was investigated with the motion quartet, a bistable stimulus for which either horizontal or vertical motion patterns are perceived. Local-level perturbations in luminance contrast affected the stability of the perceived patterns and, thereby, the size of the pattern-level hysteresis obtained by gradually changing the motion quartet's aspect ratio. Briefly eliminating luminance contrast (so nonmotion was perceived during the perturbation) eliminated pattern-level hysteresis, and briefly increasing luminance contrast (so motion was perceived during the perturbation) increased pattern-level hysteresis. Partially reducing luminance contrast resulted in bistability during the perturbation; pattern-level hysteresis was maintained when motion was perceived, and eliminated when nonmotion was perceived. The results were attributed to local motion/nonmotion perceptual decisions in area V1 affecting the magnitude of the activation feeding forward to motion detectors in area MT, where the stability of pattern-level perceptual decisions is determined by activation-dependent, future-shaping interactions that inhibit soon-to-be-stimulated detectors responsive to competing motion directions.     

Oxford cognitive screen: A critical review and independent psychometric evaluation

The Oxford cognitive screen (OCS) is a stroke-specific cognitive screening assessment. Although the test developers have provided psychometric information for the assessment, the OCS has received minimal external scrutiny, with which to triangulate the underpinning psychometrics. The purpose of this study is to provide a critical review and independent validation of the OCS. This study analysed data from an anonymised clinical database, which consisted of 316 patients who were assessed using the OCS on an Acute Stroke Unit. The rates of impairment on tests of memory and receptive communication were lower than expectation, suggesting that these subtests may be relatively insensitive. Patients with aphasia were more likely to be unable to categorised as impaired on non-language tests, suggesting that they remain sensitive to language processing or non-dominant hand usage. Some of the subtests of the OCS achieve high retest reliability, which makes them good candidates for measuring cognitive change over time. Although the OCS has many advantages, it is also important to adequately consider its limitations, that is insensitivity to memory problems, the potential confounding impact of non-dominant hand usage, and the potential that some tests may sample overall cognitive ability instead of domain-specific functioning.