Digit Position Research Articles

Manipulation After Object Rotation Reveals Independent Sensorimotor Memory Representations of Digit Positions and Forces

Planning of object manipulations is dependent on the ability to generate, store, and retrieve sensorimotor memories of previous actions associated with grasped objects. However, the sensorimotor memory representations linking object properties to the planning of grasp are not well understood. Here we use an object rotation task to gain insight into the mechanisms underlying the nature of these sensorimotor memories. We asked subjects to grasp a grip device with an asymmetrical center of mass (CM) anywhere on its vertical surfaces and lift it while minimizing object roll. After subjects learned to minimize object roll by generating a compensatory moment, they were asked to rotate the object 180 degrees about a vertical axis and lift it again. The rotation resulted in changing the direction of external moment opposite to that experienced during the prerotation block. Anticipatory grasp control was quantified by measuring the compensatory moment generated at object lift onset by thumb and index finger forces through their respective application points. On the first postrotation trial, subjects failed to generate a compensatory moment to counter the external moment caused by the new CM location, thus resulting in a large object roll. Nevertheless, after several object rotations subjects reduced object roll on the initial postrotation trials by anticipating the new CM location through the modulation of digit placement but not tangential forces. The differential improvement in modulating these two variables supports the notion of independent memory representations of kinematics and kinetics and is discussed in relation to neural mechanisms underlying visuomotor transformations.

Anticipatory Modulation of Digit Placement for Grasp Control Is Affected by Parkinson's Disease

BackgroundSuccessful object manipulation relies on the ability to form and retrieve sensorimotor memories of digit forces and positions used in previous object lifts. Past studies of patients affected by Parkinson's disease (PD) have revealed that the basal ganglia play a crucial role in the acquisition and/or retrieval of sensorimotor memories for grasp control. Whereas it is known that PD impairs anticipatory control of digit forces during grasp, learning deficits associated with the planning of digit placement have yet to be explored. This question is motivated by recent work in healthy subjects revealing that anticipatory control of digit placement plays a crucial role for successful manipulation.Methodology/Principal FindingsWe asked ten PD patients off medication and ten age-matched controls to reach, grasp and lift an object whose center of mass (CM) was on the left, right or center. The only task requirement was to minimize object roll during lift. The CM remained the same across consecutive trials (blocked condition) or was altered from trial to trial (random condition). We hypothesized that impairment of the basal ganglia-thalamo-cortical circuits in PD patients would reduce their ability to anticipate digit placement appropriate to the CM location. Consequently, we predicted that PD patients would exhibit similar digit placement in the blocked vs. random conditions and produce larger peak object rolls than that of control subjects. In the blocked condition, PD patients exhibited significantly weaker modulation of fingertip contact points to CM location and larger object roll than controls (p<0.05 and p<0.01, respectively). Nevertheless, both controls and PD patients minimized object roll more in the blocked than in the random condition (p<0.01).Conclusions/SignificanceOur findings indicate that, even though PD patients may have a residual ability of anticipatory control of digit contact points and forces, they fail to implement a motor plan with the same degree of effectiveness as controls. We conclude that intact basal ganglia-thalamo-cortical circuits are necessary for successful sensorimotor learning of both grasp kinematics and kinetics required for dexterous hand-object interactions.

Perception of Simulated Local Shapes Using Active and Passive Touch

This study reexamined the perceptual equivalence of active and passive touch using a computer-controlled force-feedback device. Nine subjects explored a 6 x 10-cm workspace, with the index finger resting on a mobile flat plate, and experienced simulated Gaussian ridges and troughs (width, 15 mm; amplitude, 0.5 to 4.5 mm). The device simulated shapes by modulating either lateral resistance with no vertical movement or by vertical movement with no lateral forces, as a function of the digit position in the horizontal workspace. The force profiles and displacements recorded during active touch were played back to the stationary finger in the passive condition, ensuring that stimulation conditions were identical. For the passive condition, shapes simulated by vertical displacements of the finger had lower categorization thresholds and higher magnitude estimates compared with those of active touch. In contrast, the results with the lateral force fields showed that with passive touch, subjects recognized that a stimulus was present but were unable to correctly categorize its shape as convex or concave. This result suggests that feedback from the motor command can play an important role in processing sensory inputs during tactile exploration. Finally, subjects were administered a ring-block anesthesia of the digital nerves of the index finger and subsequently retested. Removing skin sensation significantly increased the categorization threshold for the perception of shapes generated by lateral force fields, but not for those generated by displacement fields.

The development of short-term memory span from 8 to 16-year-old children

Objective To study the characteristic of 8 to 16-year-old children's short-term memory.Methods 157 subjects participated in this study (8,10,12,14 and 16 years old).All subjects completed the digit recall,word recall,spatial recall and position recall tests.Results Short-term memory spans increased with age (F(4,145)= 35.56,P<0.01) and peaked at 14 years old [ digit (8.83±1.31),word (4.79±0.68),spatial (5.90±0.77),position (5.42±1.28)].Conclusion The developmental trends of four tasks' memory span were similar.But the exact span-scores were different from what Pascual-Leone's model predicted. Key words: Children; Short-term memory; Development

Fingertip Replantation: Determinants of Survival

The purpose of this study was to determine the risk factors for an unsuccessful replanted fingertip. Two hundred eleven complete fingertip amputations in 211 patients who underwent replantation surgery between August of 1990 and March of 2006 were included in this study. The patients' age, gender, smoking history, digit position, dominant hand, amputation level, injury mechanism, platelet count, ischemia time, preservation method of the amputated part, anesthesia, number of arteries repaired, venous drainage, use of vein grafting, neurorrhaphy, bone shortening, and smoking after operation were tested for their impact on fingertip survival. One hundred seventy-two of 211 patients (81.5 percent) had a successful replantation. Univariate analysis showed crush or avulsion injury, high platelet count, and inappropriate preservation of the amputated part in saline solution or ethanol to be associated with a high incidence of replantation failure. Twenty-two of 54 patients (41 percent) who had a crush or avulsion trauma had failed replantation. Logistic regression analysis identified injury mechanism, platelet count, smoking after operation, preservation method of the amputated part, and the use of vein grafting as statistically significant predictive factors for success or failure. Injury mechanism, platelet count, smoking after operation, preservation method of amputated part, and the use of vein grafting were found to be the main predictors for the survival of the replanted fingertip. Applying external bleeding in zone 1 and venous drainage through the medullary cavity in zone 2 or venous anastomosis combined with vein grafting rather than venous anastomosis alone were strongly recommended in the fingertip replantation of crush or avulsion injury.

Constant-time addition with hybrid-redundant numbers: Theory and implementations

Hybrid-redundant number representation has provided a flexible framework for digit-parallel addition in a manner that facilitates area-time tradeoffs for VLSI implementations via arbitrary spacing of redundant digit positions within an otherwise nonredundant representation. We revisit the hybrid redundancy scheme, pointing out limitations such as representational asymmetry, lack of representational closure in certain adder implementations, and difficulties in subtraction and carry acceleration. Given the intuitiveness of the hybrid redundancy concept and its potential for describing practically useful redundant number systems, we are motivated to extend it within the framework of weighted bit-set encodings to circumvent the aforementioned problems. The extension is based mainly on allowing negatively weighted bits (negabits), as well as standard posibits, to appear in nonredundant positions. Our extended hybrid redundancy scheme provides for arbitrary spacing of redundant positions in symmetric digit sets, without any degradation in arithmetic efficiency, while at the same time allowing low-latency subtraction by means of the same circuitry that is used for addition. Finally, we describe how inverted encoding of negabits leads to the exclusive use of unmodified standard full/half-adder, counter, and compressor cells, with no extra inverters, and to the direct applicability of conventional carry acceleration techniques in constant-time addition.

La plastie d'expansion en Oméga « Ω ». Une nouvelle technique d'expansion des poulies annulaires du tunnel digital fléchisseur

The authors report a new technique of pulley plasty of the flexor digital system. It is not an operative procedure to reconstruct a damaged pulley but an original way to expand the volume of an intact pulley in order to adapt its volume to the diameter of the repaired flexor tendon. The flexor tendons ruptures in Verdan zone II and particularly in Tang zones IIA and IIB are often accompanied by an osteofibrous tunnel injury. Initially, the tendon sheath closure was advised after tendons repair. This sheath recovery had to have an effect on tendons nutrition by establishing the synovial cavity continuity and particularly to protect the tendons from adhesions formation. The closure of the digital tube was rapidly shown to be unnecessary creating an obstacle to the tendons movements without any effect on tendons healing. In primary tendon management, the tendon repair is associated with an increase of the tendon diameter. An incongruence appears with the surrounding digital tube with gliding resistance complicating the tendon injury recovery. In secondary tendon injury management, the flexor digital tube is subject to healing and inflammatory process. This situation with the absence of the flexor tendon generates a retraction with a collapse of the digital tunnel over the injured area. This incongruence between the repaired flexor tendons and the narrowed digital tube required a release of the retracted zone to restore an adequate volume. The only way reported is the “Venting” of a part or the total length of the pulley. This procedure even if it resolves the tendon gliding resistance, is still unacceptable. Indeed it destroys an important anatomical structure of the flexor tendon dynamic system. The flexor pulley Omega plasty “Ω” consists in releasing the lateral palmar attachment of the pulley enhancing its internal volume and increasing the flexor tendon gliding area. The digital tube is composed by the succession of five annular and three cruciform pulleys. The cruciform pulleys are thin and flexible. They retract during the digital flexion assuring the continuity of the digital tube, while the annular pulleys are thicker and fill a biomechanical function. There are two types of annular pulleys: the joint pulleys as A1, A3 and A5; they are attached to the palmar plates of the MP, PIP and DIP joints respectively. During the digital movement, they retract approximately 50% of their length. The osseous pulleys as A2 and A4 are fixed over the lateral and palmar borders of the first and the second phalanx respectively. It is on these pulleys that the Omega plasty is practised. The operative procedure is simple. It consists on a periosteal dissection over the one lateral border of the phalanx. The liberation is undergone palmarly releasing the lateral attachment of the pulley. It respects the anatomical continuity of the pulley and its mechanical properties. Indeed, the continuity of the pulley is fully respected with the periosteal flap of the digital tube floor maintaining sufficient attachment to the pulley to resist to the flexor tendon forces. The level of the flexor tendon injury and the digit position during the initial trauma will determine the level of tendon resistance and where the pulley plasty must be made. If the flexor zone II injury occurred with the digit in an extension position, the tendon conflict appears with the A2 pulley, while it arises with the A4 pulley if the digit was in flexed position. The Omega plasty creates the ideal conditions for an optimal flexor tendon movement recovery. It is a simple and a reproducible procedure. It doesn't distort the mechanical properties of the pulley and the digital tube. We used this pulley Omega plasty fifteen times in twelve patients. In 60% of the cases, the injury concerned the dominant hand, and in 67% of the cases, it was a work accident. In eight of our cases, the omega plasty was done in emergency at the same time of flexor tendon repair, while in the other seven cases, the pulley Omega plasty accompanied the late flexor tendon repair forgotten during the initial trauma management. In ten cases, the plasty concerned the A4 annular pulleys, while in the other five cases, it concerns the A2 annular pulleys. Four cases necessitate a secondary tenolysis three months after the tendon repair. Two patients moved out and cannot be included in our results. On the thirteen-remainder cases, nine retrieved a full digital flexion particularly those who underwent digital tenolysis, while the other four cases retrieved a satisfying digital function in spite of the partial DIP flexion. In our hand, the pulley Omega plasty “Ω” becomes almost a systematic procedure in conjunction with the flexor tendon repair. It offers the ideal conditions for a tendon healing and a physiological flexor tendons motion recovery.

Flexor Digitorum Profundus Tendon Tension during Finger Manipulation: A Study in Human Cadaver Hands

The purpose of this study was to measure the tension in the flexor digitorum profundus (FDP) tendon in zone II and the digit angle during joint manipulations that replicate rehabilitation protocols. Eight FDP tendons from eight human cadavers were used in this study. The dynamic tension in zone II of the tendon and metacarpophalangeal (MCP) joint angle were measured in various wrist and digit positions. Tension in the FDP tendon increased with MCP joint extension. There was no tension with the finger fully flexed and wrist extended (synergistic motion), but the tendon force reached 1.77 ± 0.43 N with the MCP joint hyperextended 45 degrees with the distal interphalangeal and proximal interphalangeal joints flexed. The combination of wrist extension and MCP joint hyperextension with the distal interphalangeal and proximal interphalangeal joints fully flexed, what the authors term “modified synergistic motion,” produced a modest tendon tension and may be a useful alternative configuration to normal synergistic motion in tendon rehabilitation.

Effect of elbow position on canine flexor digitorum profundus tendon tension

Tendon injury in the finger remains a clinical challenge to hand surgeons. A canine model is commonly used to study biological effects of tendon injuries and their treatment. There is an important anatomical difference between human and canine anatomy that may be overlooked, however, namely that most of the flexor digitorum profundus (FDP) muscle in dogs takes its origin from the medial epicondyle of the humerus, whereas in humans this muscle arises purely from the forearm. Therefore, elbow position can affect the tension of this muscle in dogs, while having no effect in humans. The purpose of this study was to measure the effect of elbow position on tendon tension in the canine digit in vitro. Elbow position had a significant effect on tendon tension. Digit motion with the elbow fully flexed resulted in significantly higher tendon tension compared to digit motion with the elbow flexed 90° or fully extended, regardless of digit or wrist position ( p < 0.05). The tension with the elbow flexed 90° was also significantly higher than with the elbow fully extended ( p < 0.05). The maximum tendon tension with the elbow fully flexed was more than eight times larger than that of the fully extended elbow ( p < 0.05). We conclude that, in the canine model, elbow position is an important parameter that affects the passive tension applied to the flexor digitorum profundus, and, by implication, to any repair of that tendon. Dog flexor tendon rehabilitation protocols should therefore specify elbow position, in addition to wrist and digit position.

How to print floating-point numbers accurately

We present algorithms for accurately converting floating-point numbers to decimal representation. The key idea is to carry along with the computation an explicit representation of the required rounding accuracy.We begin with the simpler problem of converting fixed-point fractions. A modification of the well-known algorithm for radix-conversion of fixed-point fractions by multiplication explicitly determines when to terminate the conversion process; a variable number of digits are produced. The algorithm has these properties:• No information is lost; the original fraction can be recovered from the output by rounding.• No "garbage digits" are produced.• The output is correctly rounded.• It is never necessary to propagate carries on rounding.We then derive two algorithms for free-format out-put of floating-point numbers. The first simply scales the given floating-point number to an appropriate fractional range and then applies the algorithm for fractions. This is quite fast and simple to code but has inaccuracies stemming from round-off errors and oversimplification. The second algorithm guarantees mathematical accuracy by using multiple-precision integer arithmetic and handling special cases. Both algorithms produce no more digits than necessary (intuitively, the "1.3 prints as 1.2999999" problem does not occur).Finally, we modify the free-format conversion algorithm for use in fixed-format applications. Information may be lost if the fixed format provides too few digit positions, but the output is always correctly rounded. On the other hand, no "garbage digits" are ever produced, even if the fixed format specifies too many digit positions (intuitively, the "4/3 prints as 1.333333328366279602" problem does not occur).

Two-dimensional interleaving with burst error-correcting codes

Binary two-dimensional arrays are considered, where the patches of errors contain more than one symbol from the same codeword, i.e. arrays with repetitions. The relative digit positions in each codeword are taken into account when performing interleaving, and burst error-correcting codes are used instead of random error-correcting codes.

Constant-time addition and simultaneous format conversion based on redundant binary representations

It is well-known that constant-time addition, in which the execution delay is independent of operand lengths, is feasible only if the output is expressed in a redundant representation. There are many ways of introducing redundancy and the specifics of the redundant format employed can have a major impact on the performance of constant-time addition and digit set conversion. This paper presents a comprehensive analysis of constant-time addition and simultaneous format conversion. We consider full as well as partially redundant representations, where not all digit positions are redundant. The number of redundant digits and their positions can be arbitrary, yielding many possible redundant representations. Format conversion refers to changing the number and/or position of redundant digits in a representation. It is shown that such a format conversion is feasible during (ie, simultaneous with) constant time addition, even if all three operands (the two inputs and single output) are represented in distinct redundant formats. We exploit equal-weight grouping (EWG), wherein bits having the same weight are grouped together to achieve the constant-time addition and possible simultaneous format conversion. The analysis and data show that EWG leads to efficient implementations. We compare VLSI implementations of various constant-time addition cells and demonstrate that the conventional 4:2 compressor is the most efficient way to execute constant time-addition. We show interesting connections to prior results and indicate possible directions for further extensions.

Control of grasp stability in humans under different frictional conditions during multidigit manipulation.

Control of grasp stability under different frictional conditions has primarily been studied in manipulatory tasks involving two digits only. Recently we found that many of the principles for control of forces originally demonstrated for two-digit grasping also apply to various three-digit grasps. Here we examine the control of grasp stability in a multidigit task in which subjects used the tips of the thumb, index, and middle finger to lift an object. The grasp resembled those used when lifting a cylindrical object from above. The digits either all contacted the same surface material or one of the digits contacted a surface material that was more, or less, slippery than that contacted by the other two digits. The three-dimensional forces and torques applied by each digit and the contact positions were measured along with the position and orientation of the object. The distribution of forces among the digits strongly reflected constraints imposed by the geometric relationship between the object's center of mass and the contact surfaces. On top of this distribution, we observed changes in force coordination related to changes in the combination of surface materials. When all digits contacted the same surface material, the ratio between the normal force and tangential load (F(n):L ratio) was similar across digits and scaled to provide an adequate safety margin against slip. With different contact surfaces subjects adapted the F(n):L ratios at the individual digits to the local friction with only small influences by the friction at the other two digits. They accomplished this by scaling the normal forces similarly at all digits and changing the distribution of load among the digits. The surface combination did not, however, influence digit position, tangential torque, or object tilting systematically. The change in load distribution, rather, resulted from interplay between these factors, and the nature of this interplay varied between trials. That is, subjects achieved grasp stability with various combinations of fingertip actions and appeared to exploit the many degrees of freedom offered by the multidigit grasp. The results extend previous findings based on two-digit tasks to multidigit tasks by showing that subjects adjust fingertip forces at each digit to the local friction. Moreover, our findings suggest that subjects adapted the load distribution to the current frictional condition by regulating the normal forces to allow slips to occur early in the lift task, prior to object lift-off.

Modified signed-digit addition by using binary logic operations and its optoelectronic implementation

In this work, a three-step modified signed-digit (MSD) addition by using binary logic operations is proposed. Each input digit is encoded with two binary bits. Through binary logic operations, all of the weight and transfer digits and the final sum digits represented with the same encoding scheme will be generated. The operations can be performed at each digit position in parallel. In our suggested optical arithmetic and logic unit (ALU), a single electron trapping (ET) device is employed to serve as the binary logic device. This technique based on ET logic possesses the advantage of high signal-to-noise ratio (SNR). The optoelectronic system can be constructed in a simple, compact and general-purpose form.

The stationary statistical properties of human coding sequences

We introduce a generally applicable method for the discovery and quantitation of all of the characteristic statistical properties of a class of biological sequences, given examples from the class. This method employs a reversible binary encoding of sequences into the binary digits −1 and +1. Then, provided that the sample is sufficient, the sample cumulants on the subsets of digit positions will manifest all of the statistical properties of the class. As an illustration, we present the main results of a complete characterization of the stationary statistical properties of human coding sequences, in terms of their sample cumulants. Many of the telling sample cumulants are described.

Individuated finger movements of rhesus monkeys: a means of quantifying the independence of the digits

1. Two rhesus monkeys were trained to perform flexion and extension movements of each digit of the right hand and of the wrist. Movements of all five digits and the wrist were monitored simultaneously. During each instructed movement, the instructed digit (or wrist) had the greatest excursion; other, noninstructed digits moved to varying degrees. 2. To assess the degree of independence of the different digits during these movements, I plotted, as a function of the instructed digit's position, the position of each noninstructed digit. The resulting trajectories typically were linear, with consistent slopes from trial to trial. 3. The slopes of these noninstructed digit versus instructed digit trajectories were used to calculate an individuation index for each instructed movement and a stationarity index for each digit. These indexes quantified two different aspects of independence. The individuation index reflects the degree to which other digits remained still during instructed movement of a given digit. The stationarity index reflects the degree to which a given digit remained still whenever it was a noninstructed digit. 4. In accordance with casual observation, thumb flexion and wrist flexion and extension consistently had both high individuation and stationarity and therefore can be said to be independent of the fingers. Although the same cannot be said of the other fingers, the present analysis provides a means of quantifying the degree of independence of these digits as well. 5. Factors are discussed that might contribute to the motion of noninstructed digits and to the trajectory linearity.

How to print floating-point numbers accurately

We present algorithms for accurately converting floating-point numbers to decimal representation. The key idea is to carry along with the computation an explicit representation of the required rounding accuracy. We begin with the simpler problem of converting fixed-point fractions. A modification of the well-known algorithm for radix-conversion of fixed-point fractions by multiplication explicitly determines when to terminate the conversion process; a variable number of digits are produced. The algorithm has these properties: No information is lost; the original fraction can be recovered from the output by rounding. No “garbage digits” are produced. The output is correctly rounded. It is never necessary to propagate carries on rounding. We then derive two algorithms for free-formal output of floating-point numbers. The first simply scales the given floating-point number to an appropriate fractional range and then applies the algorithm for fractions. This is quite fast and simple to code but has inaccuracies stemming from round-off errors and oversimplification. The second algorithm guarantees mathematical accuracy by using multiple-precision integer arithmetic and handling special cases. Both algorithms produce no more digits than necessary (intuitively, the “1.3 prints as 1.2999999” problem does not occur). Finally, we modify the free-format conversion algorithm for use in fixed-format applications. Information may be lost if the fixed format provides too few digit positions, but the output is always correctly rounded. On the other hand, no “garbage digits” are ever produced, even if the fixed format specifies too many digit positions (intuitively, the “4/3 prints as 1.333333328366279602” problem does not occur).

Event related potentials and electro- encephalogram in the CNV paradigm

In the brain, numbers are thought to be represented in a spatially organised fashion on what is known as the Mental Number Line (MNL). The SNARC (Spatial-Numerical Association of Response Codes) effect refers to the faster responses to digits when the reaction side is congruent with the digit position on the MNL (e.g. a left-handed response to a small magnitude) and the slowing down of responses (inhibition) in the case of incongruity. We examined the electrophysiological correlates of conflict, which are linked to that of inhibition, to shed light on the relationship between the SNARC effect and executive attention. Event-related potentials (ERPs) were recorded from twenty-nine participants during a parity-judgment task. The participants responded more quickly on congruent than on incongruent trials. The congruency effect was reflected in early sensory (N1, N2) components above parieto-occipital and frontal regions, as well as in the later P3 component above centro-parietal areas. Moreover, both the N1 amplitude and N2 latency were greater with high than low magnitude digit targets. P3 amplitude modulation implies that the SNARC effect is the result of first evoking the parallel processing of digit magnitude categorisation (in the occipital and central areas) and numeric conflict detection (in the parieto-occipital and frontal areas) and secondly conflict monitoring and resolution localised in the centro-parietal and frontal sites. These results also suggest that the left hemisphere specialises in conflict processing of high magnitude digit targets, while the right hemisphere of low digit magnitudes.

Finite approximations to infinite series

This paper is derived from lecture notes from a course in ‘object oriented programming’. They formed part of the section comparing and contrasting Smalltalk with FP systems. The work is an extension of separate published work by Knuth [1] and Turner [2]. Three types of series are considered: (a) binomial series; (b) exponential series; and (c) recurring fractions. Series may be represented as sequences of digits in an appropriate base. The choice of the base determines the nature of the series. For example, a unary representation ofe is 1∗111111...in a variable base in which the weight of a symbol is the reciprocal of the value of that digit's position in the fraction. Such a funny base can be converted to the more familiar decimal base by iteratively multiplying by ten and using the values for the overflows into the units position. Binomial series may require the use of non‐integer bases, which can be represented using rational fractions. The same methods are used as for conversion between constant integer bases. The conversion algorithm is programmed in an object oriented language which provides the support required for sequences, function parameters and rational fractions. No use is made of floating point number representation. Termination of the algorithms is discussed fully.

Memory comparison time for complex digit stimuli: The effect of number length

Woodworth (1938) reported that naming latency increased linearly with the number of digits per number (number length). In the present study, the Sternberg memory scanning paradigm was utilized to investigate this effect. It was found that the slope of the memory scanning function increased linearly with number length: memory scanning time was 40 msec for one-digit numbers, 70 msec for two-digit numbers and 101 msec for 3 digit numbers. The intercepts of the memory scanning functions did not differ for the three types of numbers. Thus the increase in latency may be due to the memory comparison stage of processing. The data suggest that a memory comparison operation occurs for each digit position of the complex memory items composed of more than one digit.