Visual discrimination of shape by octopus. squares and triangles

An experiment was performed upon visual discrimination of shape by the octopus in order to test two predictions derived from a theory of visual discrimination of orientation and shape. Two groups of octopuses were trained to discriminate between a square and a triangle and between a diamond and a triangle. It was found that octopuses discriminate more readily between a square with base horizontal and a triangle than between a diamond and a triangle. Transfer tests showed that: (1) For the octopus, an upright and an inverted triangle have more equivalence than a diamond and a square with base horizontal. (2) Octopuses do not discriminate between the figures used by analysing only differences in one part of the figures (e.g. bases or tops). (3) Having learned the initial discrimination, octopuses transfer to both larger and smaller figures. (4) A pentagon has more equivalence to a square or diamond than to a triangle. (5) A circle is not treated as equivalent to a square. The results are taken to be in agreement with the theory that octopuses analyse the vertical and lateral extents of figures, and that shape discrimination is achieved by analysing the changes in the rates of change in the firing of neurons representing the vertical and lateral extents of the shapes. The results are shown to differ from those obtained with birds and rats, but to agree with results found for higher mammals where these are available for comparison.     

An experiment on shape discrimination and signal detection in octopus

Ten octopuses were trained to perform a successive discrimination between the two shapes shown in Figure I (a). After 7 days of training, when performance was significantly above chance, transfer tests were given with other shapes that were either rotations or parts of the original training shapes. At least six theories have been put forward to explain shape discrimination in the octopus, but none of these are capable of explaining the present results. The transfer tests suggest that the discrimination was performed in terms of component parts of the shapes (vertical bars projecting upwards or downwards), and their relationship to the shape as a whole (terminal or central).

During successive discrimination training the general level of attack varies between animals, and fluctuates from day to day. As a result there are often more attacks on both the positive and negative shapes on some occasions than others, making it difficult to compare the levels of discrimination achieved. It is suggested that the concepts of signal detection theory can help overcome this difficulty. Attacks on the positive shape (“hits”) plotted against attacks on the negative shape (“false positives”) constitute an ROC curve from which a value of d', independant of the general level of attack, can be obtained.     

Visual discrimination of shape by octopus circles and squares, and circles and triangles

An investigation of the relative discriminability of circles and squares, and circles and triangles for octopus is described. The main findings were: (1) The three pairs of figures, circle and square with base horizontal, circle and square with base at 45° to the horizontal, circle and equilateral triangle were equally discriminable for the octopus. (2) Complete transfer occurred to larger and smaller figures. (3) No transfer occurred from a square in one orientation to a square rotated through 45°, nor did training with the square in one orientation lead to any saving when the discrimination was relearned with the square in the other orientation. (4) No transfer occurred from a square to a pentagon. (5) The method of training with reward on every positive trial leads to quicker initial learning of a discrimination than training with reward only where the positive figure is attacked, but discriminatory performance with the two methods approached the same asymptote. The results are in agreement with findings with other animals where these are available for comparison.     

Tactile discrimination of competing sounds

Discriminably different sounds, concurrently presented from the left and right of the medial plane, were reduced in angular separation until subjects could no longer detect which sound was “left” and which was “right.” The procedure was repeated with hearing masked and judgments made on the basis of the tactile signals at two fingertip vibrators that received their inputs from two miniature microphones bilaterally located on the subject’s head. Auditory and tactile performance were compared under active (head movements permitted) and passive (head held still) conditions. Active and passive performance were not significantly different. Auditory and tactile performance became no better than chance at angular separations of 2.7° and 4.4°, respectively. Touch compared sufficiently well with audition to support arguments for the inclusion of sound localization information in devices which use the skin as a substitute for the ear. nt]mis|This research was conducted at the Smith-Kettlewell Institute of Visual Sciences, San Francisco, California. This institute provided the apparatus for the experiment. B. L. Richardson was on Staff Development Leave from the Applied Psychology Department of the Caulfield Institute of Technology, Melbourne, Australia.     

Visual discrimination of shape by humans

Reaction times to tachistoscopic exposure and a card-sorting task are the two methods by which visual discrimination of shape is studied. The results of experiments using both methods tally, i.e. the order of difficulty of the following shapes was: (1) (easiest) circle vs. triangle; (2) circle vs. square; (3) square vs. triangle; (4) (most difficult) triangle vs. diamond. These results are compared with those obtained by Sutherland, using octopus, and it is concluded that it should be possible to establish to what extent the system of visual analysis in humans differs from that postulated for both octopus and rat.     

Comparing view sensitivity in shape discrimination with shape sensitivity in view discrimination

In three picture-picture matching experiments, the effects of a view change on our ability to detect a shape change (Experiments 1 and 2) were contrasted with the effects of a shape change on our ability to detect a view change (Experiment 3). In each experiment, both view changes and shape changes influenced performance. However, shape changes had more influence than did view changes in the shape change detection task Conversely, view changes were more influential when the task was to detect view changes. Thus, the participants could often discriminate between the effects of shape changes and the effects of view changes. The disruptive effect of task-irrelevant changes (view changes in the first two experiments; shape changes in the final experiment) does not support Stankiewicz's (2002) claim that information about viewpoint and about shape can be estimated independently by human observers. However, the greater effect of variation in the task-relevant than in the task-irrelevant dimension indicates that the observers were moderately successful at disregarding irrelevant changes.     

Tactile discrimination, response mode, and interhemispheric communication by learning disabled children.

32 right-handed, learning disabled children aged 8-10 yr., 11-13 yr., and 14-16 yr. were presented a tactile discrimination task. Pairs of fabrics of different or the same texture were presented to the same hand (uncrossed condition) or alternating hands (crossed condition). Discrimination errors were compared using a verbal response mode and a nonverbal response mode. Analysis indicated that the number of crossed errors was significantly greater in the verbal response mode than in the nonverbal response mode for only the youngest children. These results suggest selective attention-activation bias and/or hemispheric processing limitations for younger learning disabled children.     

Time course of amodal completion revealed by a shape discrimination task

We measured the extent of amodal completion as a function of stimulus duration over the range of 15–210 msec, for both moving and stationary stimuli. Completion was assessed using a performancebased measure: a shape discrimination task that is easy if the stimulus is amodally completed and difficult if it is not. Specifically, participants judged whether an upright rectangle was longer horizontally or vertically, when the rectangle was unoccluded, occluded at its corners by four negative-contrast squares, or occluded at its corners by four zero-contrast squares. In the zero-contrast condition, amodal completion did not occur because there were no occlusion cues; in the unoccluded condition, the entire figure was present. Thus, comparing performance in the negative-contrast condition to these two extremes provided a quantitative measure of amodal completion. This measure revealed a rapid but measurable time course for amodal completion. Moving and stationary stimuli took the same amount of time to be completed (≈ 75 msec), but moving stimuli had slightly stronger completion at long durations.     

Tactile discrimination performance in split-brain monkeys with secondary posterior parietal discharges

Summary Four split-brain monkeys showing EEG evidence of secondary discharges were trained to make tactile discriminations. No impairment in learning was found for the hand contralateral to the secondary hemisphere. This supports the view that epileptic discharges in the absence of cortical damage are unable to disrupt learning of tactile discrimination tasks.     

Active haptic detection and discrimination of shape

In previous research, we have shown that detection thresholds for Gaussian shapes increase with a power of 1.3 of spatial width. In the present three experiments, we generalized this finding to more complex shapes and to discrimination tasks. In Experiment 1, we found that the slope of the psychometric function for detection (i.e., distinguishing curved from flat surfaces) was independent of surface shape. In Experiment 3, we found the same result for discrimination of two different curved shapes. In Experiment 2, we found that detection and discrimination functions had the same dependence on spatial width, except that discrimination thresholds were two to four times larger. Possible neural mechanisms underlying these results are discussed.     

A test of two theories of shape discrimination

An experiment is reported which confirms a prediction from the writer's theory of shape recognition. The same experiment is held to refute an alternative theory, but this refutation is not conclusive, since the alternative theory has not been clearly stated and can be interpreted in several conflicting ways. It is shown that these possible interpretations of the alternative theory all yield predictions which are not confirmed by the present findings.     

The pigeon's discrimination of shape and location information

Two groups of pigeons (n = 4) were trained with 16 line drawings portraying a fixed shape and a variable shape. The four variable shapes (a wedge, a cone, a cylinder, and a handle) appeared to the left of, to the right of, above, or below the fixed shape (a cube). Group Shape (S) was required to discriminate the identity of the variable shape that was mated with the cube, whereas Group Location (L) was required to discriminate where the variable shape appeared relative to the cube. Three of the four pigeons in each group mastered their respective tasks. Later tests revealed that the two groups of pigeons had attended to different aspects of the shape pairs, even though the visual stimuli and general procedures they had been given were the same. Group S had attended to the identity of the variable shape and had ignored the identity and location of the cube, whereas Group L had attended to the configuration of the two shapes. The methods and stimuli could be useful in delineating the biological bases of shape and location perception.     

The visual discrimination of shape by Octopus: The effects of stimulus size

Octopuses were trained in a successive situation to discriminate between vertical and horizontal rectangles: Group S was trained with rectangles of side length 5 × 1 cm., Group M with 10 × 2 cm. rectangles, and Group L with 20 × 4 cm. rectangles. The larger the shapes used, the more readily were they discriminated, both in terms of speed of learning and of the asymptote of performance. After training, each group was given transfer tests with the two pairs of rectangles not used in training and with two further pairs of 2.5 × 0.5 cm. and 40 × 8 cm. The results can be summarized in three generalizations: (1) When the size of a shape is changed, performance is worse than on the original training shape. (2) The bigger the change in proportionate size, the less transfer is shown. (3) For corresponding changes of proportionate size, there is better transfer to larger shapes than to smaller. These generalizations are supported by data from earlier experiments on the question of transfer to different sized shapes: some of these data were reworked and are presented in detail here. The theoretical implications of the results are discussed.     

Tactile pattern discrimination at adjacent locations along the proximal-distal axis of the index finger

A discrimination task was used to examine how locations on the glabrous skin of the terminal and middle phalanges of the index finger affect the perceived shape of tactile patterns. On each trial, a pair of same-shape or different-shape patterns was presented successively on the distal half, on the proximal half, or on both halves of a phalanx. Observers responded "same" or "different" depending on the perceived pattern shape. Performance was compared between the two phalanges, with two different pattern sets. For patterns at separate locations, performance was uniformly poor. For patterns at the same location, performance was better on the distal halves than on the proximal halves of both phalanges for one pattern set but not for the other. Performance was best on the distal half of the terminal phalanx. The results are discussed in terms of the densities of innervation of first-order afferents.     

Effective 3-D shape discrimination survives retinal blur

A single experiment evaluated observers’ ability to visually discriminate 3-D object shape, where the 3-D structure was defined by motion, texture, Lambertian shading, and occluding contours. The observers’ vision was degraded to varying degrees by blurring the experimental stimuli, using 2.0-, 2.5-, and 3.0-diopter convex lenses. The lenses reduced the observers’ acuity from ?0.091 LogMAR (in the no-blur conditions) to 0.924 LogMAR (in the conditions with the most blur; 3.0-diopter lenses). This visual degradation, although producing severe reductions in visual acuity, had only small (but significant) effects on the observers’ ability to discriminate 3-D shape. The observers’ shape discrimination performance was facilitated by the objects’ rotation in depth, regardless of the presence or absence of blur. Our results indicate that accurate global shape discrimination survives a considerable amount of retinal blur.     

Generalization and discrimination of shape orientation in the pigeon

Pigeons learned to peck a green key on which parallelogram-shapes were projected; they then received generalization tests in which the orientation of the parallelogram was varied. Nondifferential training produced very little eventual stimulus control along the orientation dimension, but when training included S- trials (absence of the parallelogram) subjects responded consistently more to certain orientations than to others. Unlike typical results for visual generalization (e.g., line-tilt), the tilt gradients obtained for this complex stimulus were bimodal, supporting predictions on the basis of human perceptual data. However, unimodal gradients could be produced by specific discrimination training along the orientation dimension. Other forms of intradimensional training also produced relatively steep gradients, often characterized by unexpected but consistent secondary peaks. An attempt to obtain inhibitory gradients (S+: green key; S-: parallelogram on a green background) resulted in virtually zero responding all along the shape-orientation dimension; therefore, specific inhibitory control could not be evaluated. All these experiments suggest that definition of this complex stimulus dimension in terms of mere "angular orientation" is inappropriate, and alternative interpretations are discussed.     

Fine orientation discrimination and shape constancy in young infants

The present study aimed to investigate simultaneously fine orientation discrimination and shape constancy in young infants. The design employed two variants of the habituation paradigm. Infants in one group were habituated to a single orientation (5 or 15 degrees) of a single stimulus presented repeatedly, and they were then tested with the complementary orientation (15 or 5 degrees). Infants in a second group were habituated to several orientations (5, 10, and 15 degrees) of the same stimulus, and they were then tested with a familiar orientation of the stimulus, with two novel orientations of the same stimulus, and with a new stimulus. Between-groups comparison showed that infants habituated more efficiently to re-presentations of a single orientation than to multiple orientations of the same stimulus, providing evidence of fine orientation discrimination; posthabituation comparison within the single-orientation group confirmed that infants discriminated small orientation changes. Posthabituation comparison within the multiple-orientation group showed that infants generalized over novel orientation changes of the familiar stimulus though they discriminated change to a novel stimulus. Cumulatively, the results of this study demonstrate that under one set of conditions young infants show sensitivity to relatively fine variations in pattern orientation, but that under a different set of conditions young infants give evidence of shape constancy with the same patterns.