Routes to object constancy: Implications from neurological impairments of object constancy

Previous studies have established the existence of neurological impairments of object constancy: the ability to recognize that an object has the same structure across changes in its retinal projection. Five case studies of brain-damaged patients with deficits in achieving object constancy are reported. To test object constancy, patients discriminated two photographs of a target object, taken from different views, from a photograph of a visually similar distractor object. Four patients showed impaired matching only when the principal axis of the target object in one photograph was foreshortened. The fifth patient showed impaired matching only when the saliency of the target object's primary distinctive feature was reduced. This double dissociation suggests that normally there may be two independent means of achieving object constancy: one by processing an object's local distinctive features, the other by describing the object's structure relative to the frame of its principal axis. Neurological damage can selectively impair either process. Further, this impairment can be independent of deficits in processing visual form, since two patients with a selective deficit in the foreshortened matching task showed relatively normal form discrimination. The patient dependent on local distinctive feature information showed a deficit in size discrimination. It is suggested that this patient fails to utilize global properties of form. This failure may underlie both his impairment in achieving object constancy and in processing certain dimensions of form.     

Lesioning a connectionist model of visual search: selective effects on distractor grouping.

A connectionist model of visual search is presented, in which search is determined by patterns of grouping between distractors and between the target and the distractors. Grouping is based on conjunctive relations between simple form elements (corners, line-end terminators), and uses principles of similarity and spatial proximity. In its normal, 'unlesioned' state, the model simulates the search data generated by human subjects when they search for simple form conjunctions amongst either homogeneous or heterogeneous distractors (Humphreys & Muller, in press). In this paper, the performance of the model is examined after the model is subject to various types of 'lesion'. 'Lesioning' is produced either by increasing the internal noise on the activation functions governing the interactions between processing units, or by eliminating processing units from different loci in the model. Increasing the internal noise within the model, or lesioning units within 'high-level' processing stages, can generate the selective effects on search found in a detailed single case study of an agnosic patient (Humphreys, Riddoch, Quinlan, Price & Donnelly, this volume): Namely, there is selective disruption of search for a form conjunction amongst homogeneous distractors relative to search for the same target amongst heterogeneous distractors. This selective effect can be attributed to the 'lesion' disrupting grouping between distractors, which normally facilitates search with homogeneous distractors. The simulations demonstrate that (1) search processes can be disrupted by adding internal noise to search functions, (2) that there can be selective effects on grouping processes, and (3) that these selective effects can be associated with different types of lesion to different stages in the model. The implications of the simulations for understanding visual processing impairments in agnosia are discussed.     

Masked repetition and phonological priming in picture naming

We report a series of picture naming experiments in which target pictures were primed by briefly presented masked words. Experiment 1 demonstrates that the prior presentation of the same word prime (e.g.,rose-rose) facilitates picture naming independently of the target’s name frequency. In Experiment 2, primes that were homophones of picture targets (e.g.,rows-rose) also produced facilitatory effects compared with unrelated controls, but priming was significantly larger for targets with low-frequency names relative to targets with high-frequency names. In Experiment 3, primes that were higher frequency homophones of picture targets produced facilitatory effects compared with identical primes. These results are discussed in relation to different accounts of the effects of masked priming in current models of picture naming.     

Creating proactive interference in immediate recall: Building a DOG from a DART, a mop, and a FIG

Phonemic codes are accorded a privileged role in most current models of immediate serial recall, although their effects are apparent in short-term proactive interference (PI) effects as well. The present research looks at how assumptions concerning distributed representation and distributed storage involving both semantic and phonemic codes might be operationalized to produce PI in a short-term cued recall task. The four experiments reported here attempted to generate the phonemic characteristics of a nonrhyming, interfering foil from unrelated filler items in the same list. PI was observed when a rhyme of the foil was studied or when the three phonemes of the foil were distributed across three studied filler items. The results suggest that items in short-term memory are stored in terms of feature bundles and that all items are simultaneously available at retrieval.     

Psysquash: a program for the analysis of PsyScope data files

Many experiment-running programs generate output files that require selection, reduction, and formatting of the raw data before the numbers are suitable for input into statistical packages. PsySquash is a Macintosh program for the selection, organization, and summary of the tabular data that are produced by a widely used freeware data acquisition system, PsyScope. PsySquash serves as a bridge between PsyScope’s output data format and the input formats required by common statistical packages such as SAS, SPSS, and SuperAnova. An extension of PsySquash is proposed for use with arbitrary tabular data.     

The statistical evidence for negative transfer in part-whole free recall

A series of studies on part-whole free recall led to the conclusion that learning part of a list before learning the entire list produces negative transfer late in learning. The statistical evidence for this conclusion is shown to depend upon assumptions about (1) the asymptotic level reached and (2) the relative magnitude of the variance between conditions as compared to the variance of Ss within conditions. Evidence concerning these assumptions is reviewed, and it is argued that there was insufficient evidence to support a conclusion of negative transfer in part-whole free recall.     

Phonemic-similarity effects in good vs. poor readers

Experiments 1–4 examined immediate serial recall of rhyming and nonrhyming items by normal and poor readers in Grades 2–4. Children with generally low achievement were excluded from the poor-reader groups, so that the achievement deficit of the poor readers was centered in reading. The poor readers did not differ from the normal readers in their susceptibility to phonemic similarity either with letter lists or with word lists. Children low in both achievement and intelligence were included in Experiment 3, and they also showed normal susceptibility to phonemic similarity, except that phonemic-confusion effects were reduced when task-difficulty levels were high. Experiment 5 further demonstrated that the serial-recall task is relatively insensitive to phonemic-similarity effects when difficulty levels are high. Previous results suggesting that poor readers are relatively insensitive to phonemic similarity in such tasks may have been an artifactual consequence of marked differences in overall task difficulty for the groups compared. Implications of variations in sample-selection procedures also are discussed.     

Relevance of genotype and its environmental counterpart to the theory,interpretation, and nomenclature of ability measures

While the constructs of aplitude and achievement, which are here defined as genotypic and environmental constructs, are potentially useful in psychological theory and in the development of predictors and weights for predictors, the use of these terms for psychological tests is highly misleading. When used for tests, the terms lead to invalid inferences concerning the constructs and to erroneous predictions of later criteria. All psychological tests measure current performance levels which are phenotypic characteristics. Practically all such tests can be used to estimate both genotypic and environmental constructs with nonzero accuracy. The basic error is to use a term which denotes a genetic or an environmental construct for a phenotypic measure. Implications of this position for inferences concerning group differences in aptitude and for construct validity of tests are briefly discussed.     

Causes of racial and socioeconomic differences in cognitive tests

Correlations among profiles of means based upon 75 cognitive variables from Project TALENT are presented for groups defined by race, socioeconomic status, sex, area of the country, and grade in high school. Sex makes by far the largest contribution to differences in shape of profiles. Race and socioenconomic status, in turn, make much larger contributions to differences than grade and area. Sex differences in shapes of profiles are a function primarily of race and, to a lesser extent, of social class. Race differences are larger than socioeconomic differences and the former, in particular, are also a function of sex. Black males differ more from white patterns than black females. There is lack of substantial overlap in the causes of race and socioeconomic differences in shape of cognitive profiles.