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.     

An experiment control computer system time shared by several laboratories

An experiment control computer system, operational for more than 2 years, is discussed. The system is multiprogammed, using a vendor supplied real-time operating system. Individual experiments employ multitasking—fast response functions are implemented in core resident tasks while interactive and other slow response functions are implemented in tasks that operate under time sharing. The areas of psychological research currently supported are concept formation studies, EEG evoked response studies, monitoring the autonomic nervous system, perception studies, and family interaction studies.     

Reward vs. Reciprocity as Related to Attraction1

Groups of six subjects participated in a study to investigate the effect of obligation upon attraction. Each subject received offers of monetary aid from other members of the group. Amount of aid offered was varied along with the obligation attached to the aid. The effect of the offer upon the recipient's attraction to the donor was assessed. Both attraction and desire for coalition were greatest when the offer of aid was high and the obligation to return the benefits received was low.     

Infant search strategies with containers that move but do not alter the location at which contents can be found

A number of hypotheses about infants' delayed search accuracy have been based upon the notion that a location associated with repeated retrieval of the object attains privileged status. Infants may need strong cues to search at a new location. However, a test is reported in which performance of 12- and 15-month-old infants was shown to be indifferent to the location. The results were reliable at an individual level. The data accord with previous research upon the canonicality effect in infant spatial search, an effect which is taken to index an experiential constraint on spatial discrimination. The experimental design thus serves as a discriminative test between three approaches: the original privileged location hypothesis, a newer spatial-contrast hypothesis, and a wider approach which focuses on experiential constraints on learning, including the canonicality effect.     

Rapport pitfalls of beginning testers

Based on observations of school psychology students enrolled in a testing practicum, common pitfalls of beginning testers in the area of rapport were delineated. These pitfalls are described and illustrated with verbatim examples taken from observation notes. The authors concluded that trainees in testing often cannot translate guidelines provided in the literature into effective rapport in the testing session and that observation of test administration in a realistic setting is an essential component of supervision in testing.     

Detectability of motion as a factor in depth perception by monocular movement parallax

A display of two objects at different distances was presented to 10 observers, who were requested in two experiments to match the width of the more distant (comparison) object to the width of the nearer (standard) one under conditions permitting monocular observation and lateral head motion. The matched width of the comparison object was considered a measure of the effectiveness of movement parallax. The effectiveness of movement parallax decreases with increasing angular separation of the objects and with increasing background distance. A background without visible texture leads to a better perception of depth between two objects than a textured background The results can be explained by postulating that, whenever the detectability of motion is enhanced, i.e., the threshold for the detection of motion is lowered, the effectiveness of movement parallax as a cue to depth is increased.     

Maintaining Accurate Math Responses In Elementary School Students: The Effects Of Delayed Intermittent Reinforcement And Programming Common Stimuli.

This study examined the effect of delayed reinforcement on digits completed by elementary school children and the effect of programming stimuli common to reinforcement conditions on the maintenance of their performance. Participants exhibited similar levels of responding during intermittent and continuous reinforcement. Responding continued for a number of sessions at similar levels during a maintenance phase that included stimuli present during delayed reinforcement.