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C Morrone

Publications and source records attributed to C Morrone.

14 recordsLinked to original sources
PubMed2001

Spatiotemporal interpolation and quality of apparent motion.

We investigate the conditions under which stimuli in apparent (sampled) motion are indistinguishable from those in smooth motion and compare this discrimination with the precision achieved by the visual system in interpolating apparent motion. In an initial experiment, observers were required to discriminate smooth from apparent motion, at variable step sizes, contrasts, velocities, and stimulus types (broadband line or bar stimuli and grating patches of different spatial frequency). Thresholds for discriminating smooth from sampled motion were approximately 40 arc min under optimal conditions, corresponding to the diameter of foveal photoreceptors. The tolerated step size between stations increased with velocity, more so for low- than for high-spatial-frequency stimuli. Tolerated step size decreased with presentation duration and with stimulus contrast. A separate experiment examined precision of interpolation. Vernier offsets were produced through temporal delays along the trajectory of an apparent motion, and thresholds for the discrimination of direction of offset were measured as a function of speed of motion and of distance between stations of apparent motion. Perfect interpolation was achieved for distances between stations of approximately 2 arc min. A model based on spatiotemporal filtering at an early stage of processing accounts well for the results of both types of experiments.

Adult↗
PubMed1998

Reaction time to motion onset of luminance and chromatic gratings is determined by perceived speed.

We measured reaction times for detecting motion onset for sinusoidal gratings whose contrast was modulated in either luminance or chromaticity, for various drift rates and contrasts. In general, reaction times to chromatic gratings were slower than to luminance gratings of matched cone contrast, but the difference in response depended critically on both contrast and speed. At high image speeds there was virtually no difference, whereas at low speeds, the difference was pronounced, especially at low contrasts. At high image speeds there was little dependence of reaction times on contrast (for either luminance or colour), whereas at low speeds the dependence was greater, particularly for chromatic stimuli. This pattern of results is reminiscent of those found for apparent speed of drifting luminance and chromatic gratings. We verified the effects of contrast on perceived speed, and went on to show that the effects of contrast on reaction times are totally predictable by the perceived speed of the stimuli, as if it were perceived rather than physical speed that determined reaction times. Our results support that idea of separate systems for fast and slow motion (with separate channels for luminance and colour at slower speeds), and further suggest that apparent speed and reaction times may be determined at a similar stage of motion analysis.

Adult↗
PubMed1996

Suppression of the magnocellular pathway during saccades.

Saccades create two problems for the visual system: they cause fast (but resolvable) motion of the retinal image and a change in the relationship between retinal and external spatial co-ordinates. In this review, we examine the first of these problems, of why there is no distributing sense of motion during saccades. Recent evidence from a range of sources suggests that during saccades, the magnocellular pathway is selectively suppressed, while the parvocellular pathway is functionally unimpaired, or even enhanced. The suppression seems to occur early, possibly in the lateral geniculate nucleus, where the pathways are well separated. It is possible that the suppression shares similar mechanisms to those responsible for contrast gain control.

Animals↗
PubMed1995

[Bleeding gastric leiomyoma: diagnostic error solving an emergency case].

Although rare, benign gastric tumours are frequently encountered in the recent years thanks to the greater accuracy of diagnostic investigations. The Authors report their experience in a case of bleeding gastric leiomyoma which caused preoperative diagnostic problems due to the extraluminal development of the tumor and to diagnostic investigation errors. An easy diagnosis of this type of tumor is not therefore a rule, but, as in the case reported, may be rather insidious especially in small leiomyomas with an extra or intraparietal development and aspecific symptomatology masquereding other more frequent pathologies.

Aged↗
PubMed1981

Patterns in the discharge of simple and complex visual cortical cells.

The activity of visual cortical neurons (area 17) was recorded in anaesthetized cats in response to sinusoidal drifting gratings. The statistical structure of the discharge of simple and complex cells has been studied as a function of the various parameters of a drifting grating: spatial frequency, orientation, drifting velocity and contrast. For simple cells it has been found that the interspike interval distributions in response to drifting gratings of various spatial frequencies differ only by a time scale factor. They can be reduced to a unique distribution by a linear time transformation. Variations in the spatial frequency of the grating induce variations in the mean firing rate of the cell but leave unchanged the statistical structure of the discharge. On the contrary, the statistical structure of the simple cell activity changes when the contrast or the velocity of the stimulus is varied. For complex cells it has been found that the invariance property described above for simple cells is not valid. Complex cells present in their activity in response to visual stimuli two different firing patterns: spikes organized in clusters and spikes that do not show this organization ('isolated spikes'). The clustered component is the only component of the complex cell discharge that is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

Action Potentials↗
PubMed1981

Intra-cortical inhibition prevents simple cells from responding to textured visual patterns.

Evidence is presented that simple cells in the cat striate cortex (area 17) fail to respond to two dimensional random patterns but respond vigorously to one dimensional patterns with identical power at the preferred orientation of the cell. Further observations suggest that complex cells inhibit simple cells so as to permit them to respond selectively to one-dimensional stimuli. Implications for the role of this inhibition in visual analysis are discussed.

Animals↗
PubMed1981

Two firing patterns in the discharge of complex cells encoding different attributes of the visual stimulus.

The activity of complex neurones of area 17 was recorded in anaesthetized cats in response to sinusoidal drifting gratings of various orientations, spatial frequencies and contrasts. The responses of complex cells present two different firing patterns: spikes organized in clusters and spikes which do not show this organization ("isolated spikes"). The clustered component is the only one in the complex cell discharge which is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

Animals↗
PubMed1979

A perceptual phenomenon and its neurophysiological correlate.

A square-wave grating from which the fundamental harmonic has been subtracted (missing fundamental grating) when viewed from a suitable distance appears similar to another grating of periodicity three times higher. The neurons of the visual cortex of the cat, in a given range of spatial frequencies characteristic of each cell, give similar responses to the two gratings.

Animals↗
PubMed1979

Responses of visual cortical cells to periodic and non-periodic stimuli.

1. The activity of neurones of the visual cortex (area 17) has been recorded in anaesthetized cats in response to gratings of different profile and to single light and dark bars. 2. At very low spatial frequencies, outside the frequency response range to sinusoidal gratings, the response to square-wave drifting gratings is obtainable from a combination of the response to the single bars of the grating presented in isolation. At higher spatial frequencies this is no longer true. 3. At very low spatial frequencies the responses to square-wave gratings and to missing-fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental gratings (obtained by subtraction from the square-wave grating of its fundamental harmonic) are very similar. 4. At spatial frequencies near the peak of the spatial frequency tuning curve of the cell, the responses to square-wave grating and to sinusoidal gratings are very similar. At these spatial frequencies the response to the missing-fundamental grating is practically zero. 5. At spatial frequencies lower than that of best sensitivity for the cell, the response to square-wave gratings is correlated with the 1st and 3rd harmonic of the stimulus. 6. We conclude that at very low spatial frequencies of the grating the response of cortical cells is correlated with the light or dark edges (or light or dark bars) of the stimulus, because the edges contain high frequencies within the range of sensitivity of the cells. At higher spatial frequencies the results are interpreted best by assuming that cortical cells respond to the harmonics of the visual periodic stimulus. 7. When a background of dynamic visual noise is added to increase the spontaneous discharge of simple cells, their response to visual stimuli becomes linear or quasi-linear. The stimuli could be either single bars or gratings.

Action Potentials↗
PubMedDate not supplied

Pattern-reversal electroretinogram in response to chromatic stimuli: I. Humans.

We have studied the steady-state PERG in human subjects in response to red-green plaid patterns modulated either in luminance or in chromaticity or both. By varying the relative luminance of the red and green components, a value could be obtained at which the PERG amplitude was either minimum or locally maximum. This always occurred at equiluminance, as measured by standard psychophysical techniques. PERG amplitude and phase were measured as a function of spatial and temporal frequency of sinusoidal contrast reversal. In both space and time, the response to chromatic patterns was low-pass, while that to luminance was band-pass, and extended to higher spatial and temporal frequencies. The phase of the PERG to chromatic stimuli was systematically lagged compared with that to luminance stimuli, by an amount corresponding to about 20 ms under our experimental conditions. The variation of phase with temporal frequency suggested an apparent latency of about 67 ms for color contrast compared with 47 ms for luminance. These estimates were confirmed with separate measurements of transient PERGs to abrupt contrast reversal. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectorially the responses to appropriate luminance and chromatic contrasts, we were able to predict with accuracy the response as a function of color ratio (ratio of red to total luminance). The above findings all agree with those reported in the accompanying paper for the monkey PERG (Morrone et al., 1994), and indicate that the differences in response latency and integration time of luminance and chromatic stimuli observed by psychophysical and VEP techniques may arise at least in part from the properties of retinal mechanisms.

Color Perception↗
PubMedDate not supplied

Pattern-reversal electroretinogram in response to chromatic stimuli: II. Monkey.

We have recorded steady-state PERGs from five macaque monkeys in response to red-green plaid patterns reversed sinusoidally in contrast. The patterns had either a pure luminance contrast (red-black, green-black, yellow-black), pure red-green color contrast, or a variable amount of luminance and color contrast. By varying the relative luminance of the red-to-total luminance (color ratio) of red-green patterns, a value could be obtained at which the PERG amplitude was either minimum or locally maximum, and the phase was most lagged. This value was very similar to that producing equiluminance in human observers, and was considered to be equiluminance for the monkey. The phase of the PERG to chromatic stimulus was systematically lagged compared with that of luminance stimuli, by an amount corresponding to about 10-20 ms under our experimental conditions. The variation of phase with temporal frequency suggested an apparent latency of about 80 ms for color contrast compared with 63 ms for luminance. These estimates were confirmed with separate measurements of transient PERGs to abrupt contrast reversal. As a function of temporal frequency, the chromatic PERG function was clearly low-pass with a cutoff around 15 Hz, whereas that to luminance was double-peaked and extended to higher temporal frequencies, around 30 Hz. For both luminance and chromatic stimuli, the amplitude of PERGs increases with increasing stimulus contrast. By summing vectorially the luminance and chromatic responses of appropriate contrasts, we were able to predict with accuracy the response as a function of color ratio. In two monkeys, the optic chiasm was sectioned sagittally causing total degeneration of ganglion cells in the nasal retina, without affecting the temporal retina (verified by histology). In these animals, there was a strong response to both luminance and chromatic patterns in the temporal retinae, but none to either type of pattern in the nasal retinae, suggesting that the PERG to both luminance and chromatic stimuli arises from the inner-retinal layers. Electrophysiological studies suggest that the PERG to chromatic stimuli is probably associated with the activity of P-cells. P-cells may also make a major contribution to the PERG of luminance stimuli, although M-cells may also participate. The above findings on normal monkeys all agree with those reported in the accompanying paper for humans (Morrone et al., 1994), so similar conclusions can probably be extended to human PERG.

Animals↗
PubMedDate not supplied

[Perforation of the sigmoid caused by ingestion of foreign body].

Dating from October 1987 to January 1995 we have observed 24 patients who swallowed an extraneous object. Tree of them underwent a surgical operation whereas the remaining 21 were monitored endoscopically. Our team use to operate when the extraneous object, for its shape or dimension, comes to a stop along the intestine, causing a potential of existent complication. In 2 of the 3 cases above mentioned, the diagnosis came out from a abdomen x-ray which put into evidence a clothes peg stopped at level with the first jejunal ansa and an open pin which had performed an ileal ansa. As far as concerns the third case, we were compelled to operate without a preoperative diagnosis as the patient, mentally disabled, swallowed a sharpened, not x-rayed extraneous object (a toothpick). When swallowed, a toothpick usually causes lesions in the higher stretch of the digestive system. It is very difficult to spot the toothpick position for it slack x-opacity, even when the lesion caused by it is clearly visible. The sigma perforation, caused by the swallow of an object, rarely happens. Authors have reported a case to be pointed out for its pathogenetic originality.

Diagnosis, Differential↗
PubMedDate not supplied

[Carcinosarcoma of the gallbladder].

The authors analyse and comment on a case of carcinosarcoma of the gallbladder which they have recently observed. Given the rarity of this form of cancer, it is interesting to note that this case presents some peculiar aspects which have not been recorded in the few cases previously published on the subject. The peculiarities are such that they require a revision of what have until now been considered as intrinsic characteristics in the clinical observation of this kind of cancer. The authors maintain that the peculiarities of this case concern: a) the clinic onset of the illness and the relative aspecific symptomatology: b) that fact that laboratory tests did not signal any biochemical alteration; c) that the instrumental investigation's results pointed toward a non neoplastic pathology; d) that even the intra-operatory examination did not reveal any suspicious element; and last but by no means least the good survival of the patient which is definitely superior to other cases already reported in literature. The neoplasia, which manifested itself through a hemorrhage in the gallbladder, represented in fact the very initial stage of the illness, a condition rarely observed.

Aged↗