Attention and saccadic eye movements

Four threshold detection experiments addressed three issues concerning the relationship between movements of spatial attention and saccadic eye movements: (a) the time course of attention shifts wit saccades, (b) the response of the two systems to changes in stimulus parameters, and (c) the relationship of attention to saccadic suppression. These issues bear on the more general question of the degree of independence between the saccadic and attentional movement systems. The results of these experiments support the contention that the mechanisms that shift attention are separate from those that control saccadic eye movements. Relevant events in the visual field periphery, however, will trigger both a saccade and attention shift. The attentional response to such events does not appear to be under subjects' control. The implication of these results for theories of saccadic suppression is discussed.     

Degree of ear asymmetries for perception of dichotic chords and for illusory chord localization in musicians of different levels of competence

Left-ear superiority for perception of dichotically presented musical chords was seen in musicians at all levels of competence. However, a hypothesis that dominance would be greater in the more professional musicians was not confirmed. Whereas many of the professionals did have the largest left-ear preferences, about half had strong right-ear superiorities instead. On the average, therefore, there was no ear dominance for the two most professional groups, although the other groups had the expected left-ear dominance. Furthermore, ear differences for the professional groups were distributed only in the categories of weak to strong left- and weak to strong right-ear preferences, whereas ear differences for the other groups included also the central categories of no or little ear preference. The better musician groups were also more strongly affected by an auditory illusion in which right-ear dominance occurred when subjects reported the ear receiving the high chord, whereas left-ear dominance was seen when they reported the ear receiving the low chord (for the same dichotic pair). That is, ear dominance was dependent on instructions, switching in the same subject from left to right ear when the task changed from reporting the location of the low to reporting the location of the high chord, respectively. However, ear dominance and switching were only partially present in nonmusicians and were weak in amateurs. It may be that ear dominance for chord recognition is influenced by specialized cognitive development in musicians, on the one hand, and by noncognitive neurophysiological factors on the other.     

Psychopathy and structure of primary mental abilities

The Comprehensive Ability Battery (CAB) was used to assess 18 primary mental abilities in 53 white, male prison inmates for whom highly reliable ratings of psychopathy were available. None of the correlations between ratings of psychopathy and scores on the CAB tests was significant, and the overall pattern or structure of abilities was the same for inmates with low and high ratings of psychopathy. The possibility is raised that the personality characteristics of psychopaths make them appear to be brighter and more creative than they actually are. Compared with norms for male high school students, the inmates as a group generally performed well, falling near the 50th percentile on 11 of the tests. The inmates performed significantly better than the normative sample on tests of verbal ability, esthetic judgment, aiming, and representational drawing, and significantly worse on tests of ideational fluency, spontaneous flexibility, and word fluency.This research was supported by Grant MT-4511 from the Medical Research Council of Canada.     

Functional Differences Between Upright and Rotated Images

In Experiment I subjects imaged an alphanumeric character either upright or upside-down, and triggered a test display character. Their task was to decide as quickly as possible whether the test character was NORMAL or MIRRORED. On 72% of the trials the test was at the orientation imaged. Reaction time (RT) was then about 200 ms longer in the upside-down image condition. This difference reduced with practice. On the remaining trials the orientation of the test character differed from that of the prepared image. For upright images RT increased monotonically with the angular difference in orientation between test and image. For upside-down images RT did not increase monotonically with angular difference as there was a wide dip around the upright. Further experiments suggested that upside-down images can be rotated, but at considerably slower rates than upright ones, and that the apparent rates of rotation for upside-down images are dependent upon the width of the sector tested. These results indicate that visual short-term memory (STM) and long-term memory (LTM) are distinct; that the process of mental rotation does not operate directly upon LTM; and that functionally, upright and rotated images may differ in important ways.     

Intracranial cannulation of small animals

Special difficulties are encountered when attempting to provide intracranial cannulation of small animals that have floating or fragile skull bones. The technique described was developed for mice but seems applicable to other species. The cannula system is inexpensive and easy to use. A wound clip anchor seems superior to either skull screws or bonded acrylic, producing less damage to the brain and no necrosis of bone or tissue on the wound margin. Patency data up to 25 days is presented, and the system is as efficacious as other techniques.     

Instructions and decision times of size-constancy responses

The current study investigated the effect of instructions and stimulus discriminability on size-constancy responses and decision times in a task allowing separate evaluation of the effects of instructions and of dimensional choices by the subjects in the size-constancy task. Objective, perspective, or distance matches were influenced both by the instructions given the subject and by the relative discriminability of the stimuli in each dimension, so that subjects did not always successfully follow their instructions. Decision times were found to be fastest with perspective rather than objective or apparent instructions, but times taken to produce objective and perspective matches did not differ. Apparently, both objective and perspective judgments are available to the perceiver before a response is made, but instructions affect postperceptual response times.     

Free classification: Element-level and subgroup-level similarity

Subjects classified sets of multidimensional stimuli into two groups in any way they wished. The sets were composed of 6 or 12 stimuli: 2 or 4 instances of 3 different stimuli (e.g., 2 blue circles, 2 green circles, 2 red circles). There were striking individual differences in the preferred classification. Some subjects maximized the similarity between subgroups by matching the composition of the subgroups--one instance of each stimulus was placed in each group. The other subjects maximized the similarity among stimuli within each subgroup by placing similar stimuli in each group (the blues and greens in one group, the reds in the other). The nature of the stimuli as well as the relationships among the three stimuli had little effect on classification. In this case, cognitive styles specific to individuals but general across diverse dimensions and stimulus sets determined classification.     

Fechner’s paradox reflects a nonmonotone relation between binocular brightness and luminance

Twenty subjects judged the brightness of binocularly fused targets whose monocular luminances were varied independently. On each trial, the left eye was presented with one of two relatively high luminances and the right eye was presented with one of 15 luminances from the range in which Fechner’s paradox is effective. The objective of the experiment was to determine whether the psychophysical function over this range was nonmonotonic and Ll-shaped, as implied by several models of binocular brightness, or monotone increasing, but discontinuous at zero right-eye luminance. The functions associated with both left-eye intensities were found to be nonmonotone. Both minima were near the upper bound of the mesopic range.