Periodismo en conflicto: sin garantías ni herramientas para investigar y denunciar
4.3 Los paramilitares tienen voz en las noticias
For the perception of temperature there are two receptors, the warm and the cold. The cold receptors are more numerous than the warm, at a ratio of approximately 30:1 (Jones and Berris, 2002). These receptors respond to temperature decreases between 5 and 43°C. The warm receptors fire up to 45°C. When the skin is maintained at 30‐ 36°C, no thermal sensation is noted, although both receptors are known to fire because this is the regular skin temperature range at room temperature. When outside of this range, only one receptor will be firing at any given time. When the temperature is changing at a rate of less that 0.5°C per minute, then it is possible for the participants to not detect a change of 5‐6°C if in the 30‐36°C range. If the change is more rapid, say at 0.1°Cs¯¹, small changes in temperature can be detected. Thermal transience is thought to be perceived at a rate of 0.3°Cs¯¹ (Jones and Berris, 2002). This suggests that there is a trade‐off in warmth perception and that it is a function of both area and temperature. For example, thermal thresholds can be maintained by halving the intensity of the stimulus and doubling the contact area (Jones and Berris, 2002).
Lederman and Klatzsky (1997) state that the time to respond to thermal cues is significantly longer than encoding roughness and compliance, taking on average 900ms¯¹ to make a decision between two stimuli at different temperatures. This is consistent with the experiment carried out by Jones and Berris (2002). It took at least 200s¯¹ for the temperature of the fingerpad to stabilise after contact with the copper stimuli. Furthermore, the reported change in skin temperature was much slower than that of other published literature (Ino et al., 1993).
Ho and Jones (2004) conducted research to investigate whether participants could identify real stimuli based on their thermal properties. This experiment was also
repeated with virtual reality versions of the same stimuli using a Peltier device. The stimuli were copper, stainless steel, granite, ABS and foam, which all had the same surface roughness with the exception of the foam. A thermistor was adhered to the skin away from the pad so that it would not interfere with the touching process. No lateral scanning was permitted. The participants were shown the materials at the beginning of the experiment and asked to tell the experimenter during the experiment to say which sample they were feeling. They were blindfolded and were given no indications as to whether they were correct or not.
The ABS and foam were the most easily identified and copper was the most difficult. No reason for this was offered. For the simulated surfaces, stainless steel was the most difficult. Copper and stainless steel and granite and stainless steel were often confused. A repeated measure ANOVA was used to analyse the data and it was concluded that there was a significant effect between all stimuli. There was no significance reported between the real and simulated temperatures. Ho and Jones (2009) reported smaller decreases in the skin temperature than theoretical predictions although it was consistent with the contact coefficients (kpc) ¹/².
In an experiment investigating the effect of pressure on the temperature change of the human fingerpad, Ho and Jones (2008) investigated five pressures: 0.73kPa, 1.68kPa, 3.13kPa, 5.90kPa and 10.98kPa. The temperature changes in the fingerpad were recorded using an infra red device and with a thermistor for comparison purposes. The infra red method did appear to record more accurate information because it was able to detect finger temperature changes in the region of 3‐5°C, whereas the thermistor detected a maximum change of 0.03°C. It has been suggested that temperature change in the finger when it comes into contact with a surface is affected by pressure in 2 ways: (1) compression of the cutaneous tissue may enhance thermal sensation by increasing contact area and (2) compression can change the finger temperature by collapsing the blood vessels. There is a 70% difference in progressive blood flow from 2.9N pressure compared with 0.5N (Jay and Havenith, 2006). Repeated measures ANOVA revealed that there was a significant difference between pressures and temperature decrease, except with 1.68kPa and 5.90kPa.
A study of an aluminium beverage bottle (Han et al., 2006) presented a different view of tactile heat sensation by providing an application; optimum contact between the hands and the bottle with regards to heat transferral. The design problem presented
by Han et al. is that of a hot beverage container which will be dispensed from a vending machine at 60˚C to meet the demands of a recyclable aluminium hot beverage container in the winter months for Japanese consumers. Optimisation of the shape of the contact ribs was carried out to obtain a decrease of at least 30% of the transferral of temperature to the finger compared to the current designs. They conducted contact analysis between the hand and the ribs, showing that ribs can lessen heat transfer to the fingers. The methodology consisted of analysis of contact deformation of the finger on the proposed rib design and heat transfer analysis whilst the finger was held at a constant temperature of 35˚C.
Taking into consideration the embossing formability of the bottle, the optimum design for the bottle consisted of sharper mountains for the ribs which give a smaller contact area and no ‘bottoming out’ (Green et al. 1979) gave less contact area between the bottle and the fingers which ultimately resulted in less heat transfer. It was also concluded that this gave a better touch feeling.