The effect of retinal location on the magnitude of the Poggendorff illusion

The effect of retinal locus on the magnitude of the Poggendorff illusion was investigated. A significant illusion was found to occur in the fovea and in undiminished magnitude at the peripheral locations horizontally displaced from the fovea. No significant illusion was induced at the vertically displaced positions. It is suggested that the results obtained at the positions displaced from the fovea may be attributable to the refracting surfaces of the cornea, and that these findings lend support to an account of the Poggendorff illusion which emphasizes the significant involvement of peripheral mechanisms.     

Brightness as a function of retinal locus

Brightness functions were determined for the dark-adapted fovea and periphery. In one series of experiments, observers matched numbers to the brightness of a 1° white target at various intensities, presented half the time to the fovea, the other half to one of five peripheral loci: 5°, 12°, 20°, 35°, and 60°. In a second series, observers matched the brightness of a 1° white target in the fovea of one eye to the brightness of an identical target in the periphery of the other eye at various intensities. Thresholds were also determined for the fovea and for the five peripheral loci by a staircase procedure. The magnitude estimations and the interocular matches concur in showing that a stimulus of fixed luminance appears brighter in the periphery than in the fovea. The brightness was found to be maximal at 20°. Brightness grows as a similar power function of luminance at all six retinal positions.     

Brightness as a function of retinal locus

Brightness functions were determined for the dark-adapted fovea and periphery. In one series of experiments, observers matched numbers to the brightness of a 1° white target at various intensities, presented half the time to the fovea, the other half to one of five peripheral loci: 5°, 12°, 20°, 35°, and 60°. In a second series, observers matched the brightness of a 1° white target in the fovea of one eye to the brightness of an identical target in the periphery of the other eye at various intensities. Thresholds were also determined for the fovea and for the five peripheral loci by a staircase procedure. The magnitude estimations and the interocular matches concur in showing that a stimulus of fixed luminance appears brighter in the periphery than in the fovea. The brightness was found to be maximal at 20°. Brightness grows as a similar power function of luminance at all six retinal positions.     

Perceiving heading with different retinal regions and types of optic flow

We examined the ability to use optic flow to judge heading when different parts of the retina are stimulated and when the specified heading is in different directions relative to the display. To do so, we manipulated retinal eccentricity (the angle between the fovea and the center of the stimulus) and heading eccentricity (the angle between the specified heading and the center of the stimulus) independently. Observers viewed two sequences of moving dots that simulated translation through a random cloud of dots. They reported whether the direction of translation—the heading—in the second sequence was to the left or right of the direction in the first sequence. The results revealed a large and consistent effect of heading eccentricity: Judgments were much more accurate with radial flow fields (small heading eccentricities) than with lamellar fields (large heading eccentricities), regardless of the part of the retina being stimulated. The results also revealeda smaller and less consistent effect of retinal eccentricity: With radial flow (small heading eccentricities), judgments were more accurate when the stimulus was presented near the fovea. The variation of heading thresholds from radial to lamellar flow fields is predicted by a simple model of two-dimensional motion discrimination. The fact that the predictions are accurate implies that the human visual system is equally efficient at processing radial and lamellar flow fields. In addition, efficiency is reasonably constant no matter what part of the retina is being stimulated.     

Retinal location and visual processing rate

Although previous studies have shown that the time required to process visual stimuli increases for presentations away from the fovea, the evidence concerning the exact nature of this increase is inconclusive. Three experiments were conducted using both reaction time and tachistoscopic masking tasks to generate time-accuracy functions for stimuli at different retinal locations. All results indicated that only the time intercept parameter of the time-accuracy function is affected by retinal location of stimulation. This finding suggests that it takes longer for information to become available to some decision mechanism with stimuli displaced away from the fovea, but that the actual rate of extracting information is not influenced by retinal locus of stimulation.     

The retinal threshold gradient in the presence of a high-luminance target and in total darkness

The retinal threshold was measured along the horizontal meridian for the dark-adapted eye and for the same retinal region light-adapted by stray light from a small foveally fixated high-luminance target. This was done to quantify the irradiation phenomenon in the foveal-parafoveal boundary region. Two target luminances were investigated (5,531 and 13,000 fL). Seven Ss made threshold settings using a variable-intensity test spot whose retinal image was located at various angular separations from the foveal center as far as 10 deg in the temporal field. Threshold slopes were steeper for test spots imaged from 15min to 1 deg of arc from the foveal center than for spots imaged from ldegl5min to 10 deg of arc from the foveal center for the illuminated target conditions. The angular distance between the fovea and the intersection of the steep component with the shallow component of each threshold curve tended to shift toward the target’s edge with an increase in target luminance. These data are interpreted as an indication that a dynamic neural mechanism is involved in producing the irradiation phenomenon.     

Perceptibility of body position in anteroposterior direction while standing with eyes closed.

The perception of body position in the anteroposterior direction was investigated by evaluating the reproducibility of the position from a quiet standing posture to forward or backward leaning posture with eyes closed. The subjects were 10 healthy male undergraduates, aged 20 to 28 years. The standing position was represented by the pressure center of the foot, which was shown by the relative distance (%) from the heel to the length of the foot. The reference positions of the pressure center of the foot were set at 10% increments from 20 to 80% of the length of the foot. The subjects attempted to reproduce each reference position 10 times, and the absolute and constant errors of the reproduced position were analyzed. The absolute errors at reference positions of 30 to 60% were distinctly larger than those at the other reference positions. This indicated that the perception of standing positions from 30 to 60% was less accurate. The constant errors at the reference positions of 40 to 60% were significantly positive, which meant that the reproduced position was located farther forward than the reference position.     

On the role of refixations in letter strings: the influence of oculomotor factors

Recent studies of reading and word recognition have shown that eye-movement behavior depends strongly on the position in the word that the eye first fixates; the probability of refixating in a word is lowest with the eye near the middle of the word, and it increases as the eye fixates to either side. It has generally been assumed that the cause for this optimal landing position phenomenon lies in the very strong drop-off of visual acuity even within the fovea; refixation should be more likely when the eye starts from a noncentral position, because here less information can be extracted during one fixation. It may, however, be the case that the phenomenon is caused not by acuity drop-off, but by differences in within-word oculomotor scanning tactics as a function of the position that the eye initially fixates. To test this, in the present experiment we kept visual information constant while we varied the initial fixation position. We used homogeneous strings of letters of different length. One letter in each string was different from the rest (e.g., kkkkkok), and this was the letter that the subject initially fixated. This target letter had to be identified before saccading to a comparison string. The position of the target letter in the string was varied from trial to trial. If, owing to acuity limitations, refixations reflect insufficient information extraction, then, because the target letter is always directly fixated, the pattern of refixations in this condition should be independent of the first fixation position. However, the obtained refixation probability showed a strong dependence on the position of first fixation. The number of refixations was independent of the absolute length of the letter strings, but it seemed to be influenced by the proportion of the string over which the eye had to pass. The larger this proportion, the higher the probability of refixation. The results suggest that to a certain extent refixations in letter strings (or words) reflect properties of the oculomotor system rather than visual information extraction.     

Perceiving stimulus displacements across saccades

The visual world appears stable despite frequent retinal image movements caused by saccades. Many theories of visual stability assume that extraretinal eye position information is used to spatially adjust perceived locations across saccades, whereas others have proposed that visual stability depends upon coding of the relative positions of objects. McConkie and Currie (1996) proposed a refined combination of these views (called the Saccade Target Object Theory) in which the perception of stability across saccades relies on a local evaluation process centred on the saccade target object rather than on a remapping of the entire scene, with some contribution from memory for the relative positions of objects as well. Three experiments investigated the saccade target object theory, along with an alternative hypothesis that proposes that multiple objects are updated across saccades, but with variable resolution, with the saccade target object (by virtue of being the focus of attention before the saccade and residing near the fovea after the saccade) having priority in the perception of displacement. Although support was found for the saccade target object theory in Experiment 1, the results of Experiments 2 and 3 found that multiple objects are updated across saccades and that their positions are evaluated to determine perceived stability. There is an advantage for detecting displacements of the saccade target, most likely because of visual acuity or attentional focus being better near the fovea, but it is not the saccade target alone that determines the perception of stability and of displacements across saccades. Rather, multiple sources of information appear to contribute.     

Temporal summation in human vision: Simple reaction time measurements

Simple reaction time IRT) was measured as a function of stimulus intensity for a brief light pulse (1 msec) and a long one (300 msec). Target size, retinal position, and adapting luminance of the stimulus were varied parametrically, and the luminance value required to produce a RT of 50 msec greater than the asymptotic RT was calculated to obtain the critical duration or limit of time-intensity reciprocity. It was found that: the critical duration, even at the fovea, tends to increase with decreasing target size; the critical duration is shortest at the fovea and increases sharply with distance from the fovea; and as the adapting luminance increases, the critical duration decreases. These findings indicate that the RT technique is a sensitive measure for the stimulus conditions explored.     

Global attributes in visual word recognition: Contour perception of three-letter strings

The expetiments reported here were designed to investigate the extent to which subjects perceive the contour of three-letter strings composed of permutations of the letters (k, x) or (d, o, p). The strings were presented for 100 ms at various retinal eccentricities. 13 subjects were required to report the entire letter string. Both average contour scores and individual letter scores decrease with eccentricity. Position in the string appears to be of paramount importance, letters farthest from the fovea showing the best performance. The extensions of the letters seem to be salient cues for perceptual analysis. Shortening of the extensions causes reduced accuracy in contour recognition.     

Serial Order in Spatial Immediate Memory

Serial order effects in spatial memory are investigated in three experiments. In the first an analysis of errors in recall data suggested that immediate transpositions were the most common error and that order errors over 2 or 3 adjacent items accounted for the majority of errors in recall. The first and last serial positions are less error-prone than is the middle position in sets of six and seven items. A second experiment investigated recognition of transpositions and found that immediate transpositions were hardest to recognize but that a traditional serial position effect was not found. This may be due to the difficulty of maintaining one set of spatial items when another set is presented for comparison. A probe experiment, in which subjects were asked to recognize whether a single item came from a memory set and then to assign it to its position in the set indicated that the first and last positions were remembered more accurately than were central positions. The combination of serial order data in recall and position data suggests that there are similarities between serial order and position effects in the verbal and spatial domains and that serial order in spatial sequences is position-based.     

汉字词在不同方位与不同排列组合条件下对念读速度与准确性的影响

本研究探讨了汉字词在不同方位与不同排列组合条件下对念读速度与准确性的影响.实验结果表明逆意排列的汉字词处于不同方位(正位、左右倾斜90°、倒位),对汉字词的念读速度产生明显影响.汉字词处于正位时,念读速度最快;其次是处于左斜与右斜90°;对汉字词的念读速度最慢而准确性最低是处于倒位时(汉字词颠倒).汉字词无论是顺意排列或是逆意排列,正位结果均明显优于倒位结果;但汉字词在倒位顺意排列条件下,结果优于正位逆意排列的结果,这表明,字词间的意义联系的作用大于字词方位的作用.     

Two-pulse temporal integration functions in the fovea and peripheral retina

The temporal integration of luminous energy was compared in the fovea and at 7 degrees eccentricity using two-pulse stimuli and two methodologies. The two-pulse stimuli consisted of two 1-msec. light pulses separated by intervals of darkness ranging from 1 to 400 msec.; they were provided by a glow modulator tube transilluminating a 21.8' opal glass target. In Exp. 1 (equal-performance design), integration functions were generated using a forced-choice staircase procedure to estimate threshold luminance. The data for two Os showed that the critical duration (CD), and thus the period of complete integration, was briefer in the fovea than at 7 degrees. Beyond the CD, integration continued to differ for the two retinal locations. In the fovea, two-pulse stimuli beyond CD evidenced partial integration and at the longest stimulus durations no integration or inhibition. In contrast, at 7 degrees stimuli beyond CD appeared to evidence probability summation. In Exp. 2 (equal-energy design), integration functions were generated by measuring the detectability of two-pulse stimuli of different durations but equal in total luminous energy. A signal-detection procedure yielded measures of both response frequency and signal detectability, P(A). The data for two Os showed that for both measures CD was briefer in the fovea than at 7 degrees. Also, in the fovea, long two-pulse stimuli appeared to show no integration or inhibition. Both experiments then showed a foveal-peripheral difference in two-pulse measures of visual temporal integration, with the fovea evidencing less integration. In addition, the forced-choice and signal-detection procedures showed that these loci differences in integration were independent of the Os' response criterion.     

Discrimination of cello string height: musicianship and sex

The aim was to investigate differences by sex and music expertise in performance of a manual proprioceptive skill. Active left hand finger-movement discrimination for differences in string height was examined in a position similar to cello playing. Men and women who were experienced cellists and nonmusicians made active string depression movements and then made absolute judgments regarding which of five string positions were presented. Although no main effect was significant, analysis yielded a sex x musicianship crossover interaction (F(1,51) = 8.4, p = .006) wherein the female cellists performed better than the female nonmusicians, and the reverse occurred for males. These significant differences in active movement discrimination across sex and musicianship may be important in further understanding focal hand dystonia, a disorder wherein the interaction of sex and expertise is observed as a strong preponderance in experienced male musicians.     

Experiments on the locus of induced motion

Two experiments examined the locus of induced motion effects. The first used a subjective technique to test for the presence of retinal slippage due to systematic eye movements when an observer fixates a test spot in the center of a horizontally moving rectangle. The second experiment tested for “local” retinal effects by presenting test and inducing figures dichoptically. There was no evidence of retinal slippage under conditions where induced motion was not discriminable from real motion. Moreover, good induction was produced across eyes. Implications for the locus of induced motion effects are discussed.     

Order information in multiple-element comparison

Although it is possible to specify the elements of a list without regard to the order in which they appear, the same distinction may not be possible when the elements are retrieved from memory. To investigate this issue, we used a recognition task in which two strings of letters are presented sequentially. Subjects were instructed to respond "Same" if the second string contained the same elements as the first, regardless of their position, and to respond "Different" otherwise. Despite the fact that order information is irrelevant in this task, we observed in two experiments that reaction time for Same-item trials increased with the number of positions that the letters were displaced. Neither familiarity of the first string nor the delay between strings changed in the size of this displacement effect. To account for this finding, we propose a model in which comparison time for a given letter pair increases with the position difference of the elements in their respective strings.     

Spatial interaction effects in letter processing

The hypothesis of independent processing channels was tested in a letter-recognition task. Letter space and retinal position were varied for both unilateral and bilateral presentations of two-letter configurations. The response latencies indicated contour interference effects for small letter spaces as well as a different type of processing delay which increased rapidly with increased letter distance from the fixation point. The latter effect was assumed to represent an interaction between the feature extraction processes of the adjacent letters. Since the processing capacity decreases as a function of the distance from the fovea, the reaction times were correspondingly lengthened.     

Some visual influences on human postural equilibrium: binocular versus monocular fixation

The importance of vision for postural equilibrium has long been known; traditionally, this visual contribution to the control of posture has been analyzed primarily in terms of optical and retinal phenomena. Recently, however, there has been some suggestion that binocular and monocular fixation of identical stimuli have differential effects. Three experiments were conducted in order to measure self-generated movement (sway during quiet standing) of the body's center of gravity while field structure, ankle proprioception, and binocular/monocular fixation were varied. Field structure was varied from total darkness, to the presence of single and multiple LEDs in the dark, to full field structure (i.e., the richness of the feed back information was varied). Ankle proprioception was varied by changing foot position from side-by-side to heel-to-toe positions. Results indicate that (1) ankle-joint input is a significant factor in reducing sway, (2) binocular fixation attenuates sway relative to monocular fixation, under otherwise identical visual conditions, and (3) this difference persists in total darkness. Taken together, the data indicate that the visual influence on postural equilibrium results from a complex synergy that receives multimodal inputs. A simple optical/retinal explanation is not sufficient.     

Lateral visual masking: Supraretinal effects when viewing linear arrays with unlimited viewing time

Linear letter arrays of varying lengths were presented monocularly, binocularly, and dichoptically in order to provide locus information concerning previous findings that recognition of letters in such an array follows a U-shaped function over positions. With unlimited viewing time and constant fixation, U-shaped serial position curves were generated under all conditions of viewing. It was concluded that some supraretinal lateral masking effect is involved.